Bromo-initiators for atom transfer radical polymerization (ATRP) were successfully immobilized on the surfaces of cross-linked poly(methyl methacrylate) (PMMA) spheres by soap-free emulsion polymerization using CBr4 as the chain transfer agent. Subsequent surface-initiated ATRP (SI-ATRP) afforded a layer of PMMA brushes covalently attached to the sphere surfaces. Colloidal crystal films of these monodisperse spheres were then studied to identify the relationship between variation in particle diameter and the optical properties. The particle diameters were controlled by varying the feed monomer proportions in soap-free emulsion polymerization and the thickness of the grafted brush layer. It was found that the particle diameter could successfully be controlled to obtain crystal films that produce a variety of brilliant colors in the visible region. The results of this study can provide useful information for facile preparation of surface-immobilized ATRP initiators on colloidal polymers and can be employed for grafting polymer brushes.