I don't know about painting rotors.
First of all, if you have a part that needs to radiate heat, such as a rotor, or a radiator paint is very special.
First of all, most paints are insulators! This is bad. Only special paints should be used where heat dissipation is required.
Second, maximum radiation occurs from a black body. A reflective surface (mirrored) is THE WORST radiation surface. The best is black.
Probably the best thing on rotors would be not to paint them if you plan on getting them hot, however, who knows, there may be some special coatings that may improve heat transfer...