Monodisperse dye-doped copolymer spheres were prepared via a soap-free emulsion polymerization and swelling method. To study the relationship between the particle diameters and the optical properties of the dye-doped photonic crystals, monodisperse copolymer spheres with particle diameters varying from 581 to 98nm were prepared. When melanin dye was doped into the spheres, it efficiently reduced the light scattering inside the crystals and eliminated the iridescent effect in the photonic crystal images. The results of this study are expected to provide useful information for the synthesis of monodisperse dye-doped copolymer spheres and applications involving photonic papers.