To obtain a cured coating which has a high refractive index, is colorless and transparent, and processes excellent various types of fastness by using a colloidal dispersion (A) of a composite fine particle comprising an oxide of Sn and an oxide of Zn, an organosilicon compd. (B), and other components.

The component (A) has a particle diameter of 1 to 300mμ and the ratio of ZnO to SnO2 (by wt.) should be 0.1 to 10.0. The component (B) is a hydrolyzate and/or partial condensate of an organosilicon compd. represented by the formula R1R2aSi(OR3)3-a (R1 represents a 1-6C hydrocarbon group, vinyl, methacryloxy, mercapto, amino or epoxy; R2 represents a 1-4C hydrocarbon group; R3 represents a 1-8C hydrocarbon group, an alkoyxyalkyl, or acyl; and a is 0 or 1) (e.g. methyltrimethoxysilane). The above two components are used as indispensable components, and other components are added for improving the properties of a coating fluid and imparting functions to the cured coating.