So currently, the planets colors are determined by cosmetic settings. But there could be a switch that toggles between cosmetic and composition, which means for example if the planet is mostly water ice, the planet will be blue-white, if the planet is mostly iron, its more red-grayish. Just an optional switch to toggle in planet studio.
I think this really is a great idea! Also, you could put elements, like if you want a literal Carbon Planet, or a metal world.