BACKGROUND

[0001] There are various types of three-dimensional (3D) printing technologies, including, for example, stereolithography, fused deposit modeling, and the like. 3D printing typically includes building a 3D object from a computer-aided design model, additive manufacturing file, or the like. Some 3D printing technologies allow for full-color 3D printing.

[0002] Designers may specify colors for 3D objects within a standardized color space. For example, a designer may specify a color using Red Green Blue values corresponding to specific colors in the sRGB color space. In other instances, designers may specify colors using other values within other color spaces.

BRIEF DESCRIPTION OF THE DRAWINGS [0003] Non-limiting and non-exhaustive examples of the disclosure are described herein, including various examples of the disclosure illustrated in the figures listed below. [0004] Figure 1 illustrates an example of a color reference object with removable sub objects in a three-dimensional (3D) array corresponding to a color space cube.

[0005] Figure 2 illustrates an example removable sub-object of a color reference object corresponding to a color space cube.

[0006] Figure 3 illustrates an example color reference object with a vertical layer pivoted with respect to other layers to provide access to the removable sub-objects. [0007] Figure 4 illustrates an example of a removable, discrete sub-object secured to a framework of a color reference object.

[0008] Figure 5 illustrates multiple vertical layers of an example color reference object pivoted with respect to one another.

[0009] Figure 6A illustrates an example sub-object in the shape of a tetrahedron.

[0010] Figure 6B illustrates an example sub-object in the shape of a cube.

[0011] Figure 6C illustrates an example sub-object in the shape of a hexagonal prism.

[0012] Figure 6D illustrates an example sub-object in the shape of an octahedron. [0013] Figure 6E illustrates an example sub-object in the shape of a truncated octahedron.

[0014] Figure 6F illustrates an example sub-object in the shape of a dodecahedron. [0015] Figure 7A illustrates an example sub-object with L ^* a ^* b ^* color values representing the color of the sub-object in the 1976 CIE (L ^* a ^* b ^* ) color space on one face. [0016] Figure 7B illustrates the example sub-object with L ^* a ^* b ^* color values on one face rotated.

[0017] Figure 7C illustrates another view of the example sub-object with an electronically readable code on one face.

[0018] Figure 7D illustrates a bottom view of the example sub-object with RGB color values representing the color of the sub-object in the sRGB color space on a bottom face. [0019] Figure 8 illustrates another example of a color reference object with horizontally separable layers.

[0020] Figure 9 illustrates a block diagram of an example computing system in communication with a 3D printing system for 3D printing a color reference object corresponding to a digital color object representing a color space.

DETAILED DESCRIPTION

[0021] A designer of a three-dimensional (3D) object for 3D printing via a 3D printing system may select various colors for various parts of the 3D object. Each color may, for example, be selected on an electronic display as part of a computer-aided design process. Designers may specify colors using numerical values corresponding to standardized color spaces. For example, a designer may specify a color by entering numerical red, green, and blue values identifying a color within the sRGB color space. In some instances, a designer may select a displayed color from a gamut of available colors. In some instances, a designer may select a color within a digital color space cube representing the sRGB color space.

[0022] A graphical user interface may display the 3D object with the selected colors on an electronic display (e.g., a computer monitor or television). The designer may print the 3D object via a 3D printing system and find that the colors of the printed 3D object do not match the colors displayed on the electronic display. To obtain a printed 3D object with the desired colors, the designer may have to print several iterations of the 3D object with slight variations in color selection. Even with a color-calibrated monitor and a color managed print preview, it can be difficult to visualize exactly how printed colors will appear once they are printed via a 3D printing system. Furthermore, a designer may not fully comprehend or appreciate the gamut of colors available via a specific 3D printing system, including specific printing hardware, printing materials, and printing parameters.

[0023] This disclosure includes various examples and variations of physical color reference objects that may be printed via a 3D printing system. In some examples, a physical color reference object may be 3D printed to showcase the achievable colors of the 3D printing system and/or facilitate a visual mapping between colors selected on a monitor in a digital color space and real-world print colors produced by the 3D printing system. In various examples, a color reference object includes a framework to house a 3D array of discrete sub-objects that can selectively be removed from the framework. The discrete sub-objects may, for example, be polyhedron sub-objects that are each printed with a uniform color and arranged within the framework to correspond to a color space volume, such as an sRGB color space cube.

[0024] The framework may include multiple layers that can be separated from one another. For example, vertical layers may be hinged or slidably separable from one another, or horizontal layers may be slidably removed like drawers from the framework. Each discrete sub-object may include a securing mechanism, such as a clip, to secure each discrete sub-object within the framework in a 3D array with colors corresponding to a digital color space volume (e.g., an sRGB color space cube or a 1976 CIE (L ^* a ^* b ^* ) color space volume). In some examples, the color reference object may include a closure mechanism to selectively secure the vertical or horizontal layers in a closed state (e.g., in a cuboid shape).

[0025] In one specific example, the framework comprises five vertical layers that can be, at least partially, separated from one another. Each layer includes 25 polyhedron sub objects in a 5 x 5 arrangement, such that the entire 3D color reference object includes 125 polyhedron sub-objects arranged in a cube shape with 5 polyhedron sub-objects on each side. The five separable layers may be hinged with respect to one another so that a user (e.g., a designer) can access polyhedron sub-objects within the 3D cubic array of polyhedron sub-objects. The polyhedron sub-objects are printed with colors so that the 3D cubic array of polyhedron sub-objects corresponds to a digital color space cube (e.g., an sRGB color space cube, CIE (L ^* a ^* b ^* ) color space volume, or the like). Thus, the example 3D cubic array of polyhedron sub-objects may include 125 discrete, polyhedron sub-objects arranged by color to correspond to an sRGB color space cube that may include many millions of discrete colors.

[0026] For instance, a 24-bit sRGB model includes 256 discrete levels of color per channel for a total of 16.7 million colors. An sRGB color space cube may appear to have nearly continuous color transitions between six corners of red, blue, green, cyan, black, white, yellow, and magenta. In the example above, the polyhedron sub-objects may be arranged by color to correspond or approximate the sRGB color space cube by including corner polyhedron sub-objects that are red, blue, green, cyan, black, white, yellow, and magenta. With a 5 x 5 x 5 array of polyhedron sub-objects, three polyhedron sub-objects are positioned between each of the corner polyhedron sub-objects and colored to correspond to a discretized sRGB color space cube.

[0027] The framework may include a different number of separable layers and/or a different number of discrete sub-objects in each layer. Specifically, the framework may include N separable layers, where N is an integer value. Each layer may include N ² discrete sub-objects in an N x N layout, such that the framework includes N ³ discrete sub objects arranged in a 3D cube shape with N discrete sub-objects on each side. A larger number of discrete sub-objects provides increased granularity with smaller discrete sub objects for a color reference object of a given size.

[0028] In examples in which polyhedron sub-objects are utilized, the polyhedron sub object may have any number of faces with normal vectors in distinct directions relative to the 3D print manufacturing process. As previously described, each polyhedron sub-object may be printed with a single, uniform color and arranged such that the collective 3D array of polyhedron sub-objects resembles a discretized approximation of a color space volume of a standardized color space. However, even though each polyhedron sub-object is 3D- printed with a solid color, the different faces of the polyhedron sub-objects may each exhibit slight color variations due to the inherent manufacturing process of 3D printing. For example, the top face of a cube may appear to have a slightly different color than the bottom face of the cube due to the 3D printing technology.

[0029] Larger faces on a polyhedron sub-object may make it easier for a designer to visually distinguish the color variations between different faces. Each face with a normal vector in a distinct direction provides unique color variation information for a given color. Accordingly, the polyhedron shape may be selected to provide many distinct faces while ensuring that each distinct face is large enough to facilitate visual color comparison between the various faces. Thus, larger polyhedron sub-objects may be 3D printed to have more faces than smaller polyhedron sub-objects.

[0030] In various examples, each discrete sub-object may include a label identifying the color of the discrete sub-object. For example, RGB values may be printed (e.g., in another color or as an embossing/debossing in the surface) that identify the color of the discrete sub-object in the sRGB color space. In some examples, electronically readable information may be included on each discrete sub-object that identifies the color of the discrete sub-object in one color space or in multiple color spaces. In various examples, each discrete sub-object may include multiple identifying marks that each identify the color of the discrete sub-object in a different color space.

[0031] The discrete sub-objects in a color reference object may be selected to be spheres, cubes, rectangular prisms, tetrahedrons, octahedrons, dodecahedrons, icosahedrons, truncated octahedrons, etc. Due to the finite print resolution of 3D printing systems, at the extreme end of the spectrum, a polyhedron sub-object may approximate a sphere. However, it may be difficult to distinguish the color variations of the different faces on a polyhedron sub-object that approximates a sphere since each “face” may be as small as the print resolution of the 3D printing system in any given print direction. In some examples, a designer may not be concerned by the color variations of different faces, and so a spherical sub-object, or even a sub-object approximating a sphere, may be suitable. In some examples, a spherical or ellipsoidal sub-object may include flattened faces to exhibit color variations based on 3D print directions.

[0032] Accordingly, the shape of each discrete sub-object, the size of each discrete sub-object, and the number of discrete sub-objects included in a color reference object may be selected to provide a target balance of (i) color granularity relative to a continuous color space volume, (ii) the number of faces, if any, on a discrete sub-object to illustrate print-direction color variations, and (iii) the size of each distinguishable face on the polyhedron sub-object.

[0033] A computer associated with a 3D printing system and/or a controller within a 3D printing system may include a non-transitory computer-readable medium with instructions stored thereon to facilitate 3D printing a color reference object, according to any combination of the examples described herein to showcase the color range of a particular 3D printing system. In other examples, the non-transitory computer-readable medium may include instructions to facilitate printing a color reference object to provide a designer a physical object to visualize 3D printed material colors corresponding to colors selected on a digital color space cube or colors specified by numerical values defined in a specific color space.

[0034] The color reference object may include discrete sub-objects identified or identifiable in any of a wide variety of color spaces, including, without limitation the CIE (L ^* a ^* b ^* ) color space, the sRGB color space, an Adobe RGB color space, a CIEXYZ color space, a ProPhoto RGB color space, or another color space. The color of each discrete sub-object may be identified or identifiable in any number of different color spaces and may include machine-readable and/or human-readable markings identifying the color in one color space or in multiple color spaces. The 3D color reference object may include discrete sub-objects arranged to correspond to a color space volume of any selected color space.

[0035] Many of the examples illustrated and described herein refer to a color space cube. However, it is appreciated that many of these examples may be adapted to accommodate color space volumes other than cubes. For example, a color reference object may include discrete sub-objects colored and arranged in a 3D array within a framework forming a rectangular prism or cuboid whose faces are not all squares. In another example, a color space volume occupying a portion of the CIE (L ^* a ^* b ^* ) color space may be irregular shaped and a corresponding color reference object may include discrete sub-objects colored and arranged in a 3D array within a framework corresponding to the irregular shape. [0036] For example, an sRGB color gamut may be transformed into the CIE 1976 (L ^* a ^* b ^* ) color space. The shape of the transformed gamut is irregular since the sRGB color gamut occupies only a portion of the CIE 1976 (L ^* a ^* b ^* ) color space. The irregular gamut can be discretized and the corresponding L ^* a ^* b ^* values can be used as labels on the discrete sub-objects of the color reference object. In an alternative example, an sRGB cube is utilized and the sRGB color space is discretized, but corresponding L ^* a ^* b ^* values are calculated and used to label each discrete sub-object of a color reference object. In such examples, the colors of the discrete sub-objects are related to specifications of input colors. However, in many instances, a selected color (regardless of the color space in which it is specified) is transformed into RGB color values in the sRGB color space prior to transmission to a 3D printing system.

[0037] As another example, a color space volume may have a rectangular prism shape with one dimension larger than the others. A color space rectangular prism with one dimension longer than the others may be used to represent a gamut of colors available in a 3D printing system with four or more base or primary print colors. A color reference object may be printed to include discrete sub-objects arranged in an N x M x L array in which N, M, and L are integer values that may or may not be equal.

[0038] In various examples, a designer may remove a subset of discrete sub-objects from the color reference object as part of a color palette selection process. The ability to remove a subset of discrete sub-objects from the color reference object allows the designer to see the different colors side-by-side. The designer may utilize a software program to design a 3D object and specify various colors for various portions of the 3D object to match those of the selected discrete sub-objects within the color palette. The color reference object allows the designer to know how the colors of the 3D object designed on the computer and displayed via an electronic display will actually appear once the 3D object is 3D printed via the 3D printing system.

[0039] The examples of the disclosure may be further understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components of the disclosed examples, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the examples of the systems and methods of the disclosure is not intended to limit the scope of the disclosure, as claimed, but is merely representative of possible examples of the disclosure. In addition, the elements of a method do not necessarily need to be executed in any specific order, or even sequentially, nor do the elements need to be executed only once, unless otherwise specified.

[0040] In some cases, well-known features, structures, or operations are not shown or described in detail. Furthermore, the described features, structures, or operations may be combined in any suitable manner in various examples. It will also be readily understood that the components of the examples as generally described and illustrated in the figures herein could be arranged and designed in a wide variety of different configurations. [0041] Several aspects of the examples described may be implemented as software modules or components. As used herein, a software module or component may include any type of computer instruction or computer-executable code located within a memory device and/or transmitted as electronic signals over a system bus or wired or wireless network. A software module or component may, for instance, comprise multiple physical or logical blocks of computer instructions, which may be organized as a routine, program, object, component, data structure, etc., that performs tasks or implements particular abstract data types.

[0042] In certain examples, a particular software module or component may comprise disparate instructions stored in different locations of a memory device, which together implement the described functionality of the module. Indeed, a module or component may comprise a single instruction or many instructions and may be distributed over several different code segments, among different programs, and across several memory devices. Some examples may be practiced in a distributed computing environment where tasks are performed by a remote processing device linked through a communications network. In a distributed computing environment, software modules or components may be located in local and/or remote memory storage devices. In addition, data being tied or rendered together in a database record may be resident in the same memory device, or across several memory devices, and may be linked together in fields of a record in a database across a network. [0043] Examples may be provided as a computer program product, including a non- transitory computer and/or machine-readable medium having stored thereon instructions that may be used to program a computer (or another electronic device) to perform processes described herein. For example, a non-transitory computer-readable medium may store instructions that, when executed by a processor of a computer system, cause the processor to perform certain methods disclosed herein. The non-transitory computer- readable medium may include, but is not limited to, hard drives, floppy diskettes, optical disks, CD-ROMs, DVD-ROMs, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, solid-state memory devices, or other types of machine-readable media suitable for storing electronic and/or processor-executable instructions.

[0044] Figure 1 illustrates an example of a 3D-printed color reference object 100 with removable sub-objects 120 in a 3D array corresponding to a digital color space cube 151 . A block diagram 160 shows an example color space cube in which red, green, and blue are used as primary colors and defined along the three axes. Any of a wide variety of colors can be selected by mixing the three primary colors. In some examples, the color reference object 100 is 3D printed via a 3D printing system to showcase the achievable colors of the 3D printing system. The color reference object 100 may additionally or alternatively be 3D printed by the 3D printing system to provide a visual mapping between electronically displayed colors and physical, printed colors.

[0045] For example, a designer may utilize a software program to design a 3D object for 3D printing. A window 150 of the software program may enable a designer or other user to select a color for a particular part or portion of a 3D object. For example, the designer may click a color on a rotatable digital color space cube 151 or manually enter red (R), green (G), and blue (B) values defined within a specific color space, such as the sRGB color space.

[0046] The designer may visualize the selected color on an electronic display (e.g., a computer monitor or television). A printing system may utilize a perceptual color transformation to map digitally assigned color values (e.g., sRGB color values) to ink quantities and/or color material mixing ratios during the 3D print process. Flowever, as described above, the colors of a 3D-printed object may not exactly match the colors displayed on an electronic display. Even with a color-calibrated monitor, it may be difficult to visualize how printed colors will appear once they are printed via a 3D printing system. [0047] Accordingly, the designer may use the color reference object 100 to visualize how specific colors specified within a standardized color space cube will appear once printed by a particular 3D printing system. As illustrated, the color reference object 100 may include a framework 110 divided into five vertical layers 111 , 112, 113, 114, and 115. In the illustrated example, each vertical layer 111 -115 includes a two-dimensional array of 25 polyhedron sub-objects 120, such that the entire color reference object includes a 3D array of 125 polyhedron sub-objects 120 in a 5x5x5 cube shape.

[0048] In the illustrated example, each polyhedron sub-object 120 is a truncated octahedron with a securing mechanism (illustrated as a clip) to secure the polyhedron sub-object in its place within the framework 110. Each polyhedron sub-object 120 is printed to have unique, uniform color and arranged within the framework so that the collective 3D array of sub-objects 120 corresponds to a color space cube, such as the color space cube in the block diagram 160. The different colors of polyhedron sub-objects 120 are illustrated in the figures using different fill patterns, but no specific fill pattern is intended to correspond to any specific color. Rather, the color reference object 100 is labeled with Red, Green, and Blue axes to show the correlation with the axes of the color space cube in the block diagram 160. The color reference object 100 may be adapted to include discrete colors of polyhedron sub-objects 120 selected to correspond to any of a wide variety of color spaces.

[0049] Figure 2 illustrates an enlarged view of an example polyhedron sub-object 220 removed from a color reference object 200 corresponding to an sRGB color space cube. The illustrated color reference object 200 includes a plurality of discrete, polyhedron sub objects, such as polyhedron sub-object 220, secured within a framework 210. In the illustrated example, the polyhedron sub-object 220 is a truncated octahedron with 14 faces (8 regular hexagonal faces and 6 square faces). Faces 221 , 222, 223, and 224 are visible, while face 225 and other faces on the backside of the polyhedron sub-object are not visible.

[0050] The polyhedron sub-object 220 includes a securing mechanism in the form of a clip 230 to selectively secure the polyhedron sub-object 220 to a rail within the framework 210 of the color reference object 200. The clip 230 may be 3D printed to include an aperture 231 to increase the flexibility and/or resiliency of the clip 230.

[0051] Figure 3 illustrates an example color reference object 300 with a vertical layer 311 pivoted with respect to four other vertical layers 312, 313, 314, and 315. The other four vertical layers 312-315 may also be pivotable but are illustrated in a closed position. The vertical layer 311 may be transitioned from the closed, cube shape illustrated in Figure 2 to an open, pivoted state by pivoting the vertical layer 311 about a hinge 318 with respect to the four other vertical layers 312-315. In some examples, the hinge 318 may be 3D-printed integral with other portions of the framework 310. Each of the vertical layers 311-315 may be selectively pivoted with respect to adjacent vertical layers to allow a user to view, access, and/or remove discrete sub-objects 320 from the framework 310 of the color reference object 300.

[0052] Similarly, each of the discrete sub-objects 320 may be 3D-printed at the same time as the framework 310. Each discrete sub-object 320 may be selectively removable from the framework 310 of the color reference object 300. As in other examples, the various discrete sub-objects 320 are illustrated with various shadings to represent the color transitions between the corners of the color reference object 300, which are selected such that the cumulative 3D array of discrete sub-objects 320 corresponds to a color space cube. For example, the illustrated 3D array of 125 discrete sub-objects 320 approximates a discretized sRGB color space cube.

[0053] Figure 4 illustrates an example of a removable, discrete sub-object 420 secured to a rail 439 of a framework 410 of a color reference object 400. As illustrated, the discrete sub-object 420 is 3D printed to include a securing mechanism as a clip 430 that allows users to selectively secure and remove the discrete sub-object 420 from the framework 410.

[0054] Figure 5 illustrates multiple vertical layers 511 , 512, 513, 514, and 515 of an example color reference object 500 pivoted with respect to one another. The five vertical layers 511-515 may be connected by hinges 518 that are integral with or fitted to the framework 510 of the color reference object 500. In the closed state (as illustrated in Figure 2), the color reference object 500 includes discrete sub-objects in a cube shape with unique colors arranged so that the color reference object 500 corresponds to a color space cube of a selected color space, such as an sRGB color cube representing the sRGB color space. The color reference object 500 may include closure mechanisms 519 to allow a user to secure the vertical layers 511-515 in a closed position.

[0055] Internal discrete sub-objects can be viewed and/or accessed by opening the various vertical layers 511-515. In alternative examples, the hinges 518 may be omitted from the color reference object 500 so that the vertical layers 511-515 can be completely separated from one another. In some examples, the discrete sub-objects may be removable from only one face (an access face) of each vertical layer. The framework 510 may prevent the discrete sub-objects from being removed from the other, non-access face of each vertical layer. In alternative examples, discrete sub-objects may be removed from either face of a vertical layer.

[0056] Figure 6A illustrates an example sub-object as a tetrahedron sub-object 621 with a clip 631 for selective attachment to a framework of a color reference object.

[0057] Figure 6B illustrates an example sub-object as a cuboid sub-object 622 with a clip 632 for selective attachment to a framework of a color reference object.

[0058] Figure 6C illustrates an example sub-object as a hexagonal prism sub-object 623 with a clip 633 for selective attachment to a framework of a color reference object. [0059] Figure 6D illustrates an example sub-object as an octahedron sub-object 624 with a clip 634 for selective attachment to a framework of a color reference object.

[0060] Figure 6E illustrates an example sub-object as a truncated octahedron sub object 625 with a clip 635 for selective attachment to a framework of a color reference object.

[0061] Figure 6F illustrates an example sub-object as a dodecahedron sub-object 626 with a clip 636 for selective attachment to a framework of a color reference object. Figures 6A-6F illustrate a few example shapes of sub-objects, but it is appreciated that any of a wide variety of shapes and sizes are possible.

[0062] Figure 7A illustrates an example truncated octahedron sub-object 720 with a clip 730 to facilitate selective attachment and removal of the truncated octahedron sub object to a framework of a color reference object. A first face 721 of the truncated octahedron sub-object 720 may include a label with numerical L ^* a ^* b ^* values identifying the color of the truncated octahedron sub-object 720 in a CIE (L ^* a ^* b ^* ) color space. Clip 730 and blank faces 722 and 723 are labeled in Figures 7A-7D to facilitate an understanding of the rotation of the truncated octahedron sub-object 720 in each figure. [0063] Figure 7B illustrates the example truncated octahedron sub-object 720 rotated to the right slightly so that the labeled face is on the right side. The blank faces 722 and 723 are no longer visible.

[0064] Figure 7C illustrates the example truncated octahedron sub-object 720 rotated further so that a rear face 725 is visible with a machine-readable value (in the form of a QR code) that identifies the color of the truncated octahedron sub-object 720 in a color space. The blank face 722 is visible

[0065] Figure 7D illustrates a bottom view of the truncated octahedron sub-object 720 with RGB color values on a bottom face 724 that identifies the color of the truncated octahedron sub-object 720 in the sRGB color space. The blank face 723 is visible on the truncated octahedron sub-object 720.

[0066] Figure 8 illustrates another example of a color reference object 800 with horizontal layers 811 , 812, 813, 814, and 815 configured as slidable drawers within a framework 810. In the illustrated example, each horizontal layer 811 -815 can be slidably opened by removing it from the framework 810. The top three horizontal layers 811 -813 are closed. The fourth horizontal layer 814 is partially opened, and the bottom horizontal layer 815 is slightly more opened. Once opened, the discrete sub-objects 820 may be selectively removed from the color reference object 820. Collectively, the discrete sub objects are arranged in a 5 x 5 x 5 array of discrete sub-objects 820 with colors selected to correspond to those of a color space cube, such as an sRGB color space cube or CIE (L ^* a ^* b ^* ) color space cube.

[0067] Each of the discrete sub-objects 820 may be labeled with a unique numerical value identifying the color of the discrete sub-object 820 within a color space. In the illustrated example, the color reference object 800 may include a floor in each horizontal layer 811-815, depressions or protrusions in the floor of each horizontal layer 811 -815, rails, and/or other framework components to function as securing mechanisms that removably secure each discrete sub-object in a fixed location within the framework 810. [0068] Accordingly, a designer may open a horizontal layer 811-815 and remove a discrete sub-object 820. The designer may read the numerical values identifying the color of the removed discrete sub-object 820. The designer may input the numerical values into a 3D design software to assign the color to portions of a 3D object design. The designer can be confident that once the 3D object is printed, the color of the portions assigned the numerical color values will match the color of the removed discrete sub-object 820. [0069] Figure 9 illustrates a block diagram of an example computing system 910 in communication with a multicolor 3D printing system 990 for 3D printing a color reference object corresponding to a digital color object representing a color space. A controller 912, such as a processor or hardware circuitry, a memory 914, and/or a communication interface 916 may be in communication with a computer-readable storage medium 950 via a bus 902. The computer-readable storage medium 950 may include a digital color space module 952 that stores a standardized color space or multiple standardized color spaces. Each standardized color space identifies distinct colors using numerical values. For example, an sRGB color space may identify each of a plurality of colors using Red, Green, and Blue values. The color space may be used by 3D design software to specify colors of portions of a 3D object digitally created by the designer. The digital color space module 952 may generate a digital color space cube to aid the designer in visualization and/or selecting colors during the design of a 3D object.

[0070] A printer interface module 954 may communicate the 3D object digitally created by the designer to the multicolor 3D printing system 990 for manufacturing by a 3D printing process. As discussed above, colors selected by the designer via the digital color space module 952 may be displayed on an electronic display during the digital creation process. Flowever, the colors displayed on the electronic display may not match the colors of the printed object.

[0071] Per the examples described herein, the designer may use the physical reference object module 958 to cause the multicolor 3D printing system 990 to print a color reference object. For example, the physical reference object module 958 may cause the multicolor 3D printing system 990 to print a color reference object that includes a framework and a plurality of discrete sub-objects removably secured within the framework. The discrete sub-objects may be arranged in a three-dimensional array with colors corresponding to those of the digital color space cube generated by the digital color space module 952. [0072] Once the color reference object is printed, the designer can select colors for a 3D object design by identifying numerical values labeled on a sub-object of the color reference object selected by the designer.

[0073] While specific examples and applications of the systems and methods described herein are illustrated and described in detail, the disclosure is not limited to the precise configurations and components as described. Many changes may be made to the details of the above-described examples without departing from the underlying principles of this disclosure. The scope of the present disclosure should, therefore, be understood to encompass at least the following claims.