To provide a method of preparing a coloring material which can obtain the target visible light spectral data from a designated chromaticity value.

First, a starting material is fixed and with the use of the previously measured visible light spectral data, a procedure for synthesizing spectral data (a method of allowing peaks to move in the wavelength direction, a method of allowing peaks to move in the transmittance direction, a method of randomly varying the transmittance) is selected. Next, the conditions relating to the wavelength to be controlled and the transmittance to be varied or the upper and lower limits of the wavelength and knurling are inputted, and the transmittance data for every wavelength are varied to produce spectral data and a chromaticity value is calculated from the synthesized spectral data to compare the color difference with the target chromaticity value, and calculations of the spectral synthesis and the chromaticity value are repeated until the color difference comes to a specified value or below, and when the color difference comes to the specified value or below, the visible light spectral data of a dye approximate to the designated chromaticity value can be obtained.