Color variation is based on hair color. Yes player and slave just 1:1 so can make copies you could say.
How the color works in the game is rather simple it scales based on Light/Dark and then it follows an actual color template.
Client hair color is random and cant see what their hair color is. If you have a blue hair slave and they breed with a yellow or red hair client they get that respective color blend of purple or green depending on the light and darkness. Now if its like orange and blue most likely be brown. Now for white and black you just have to get the colors as light or dark and get them to the point it says white or black. There is grey also.
Skin colors you have to either get from a new slave or modify current ones.
Currently known hair colors Blue, Cyan, Green, Yellow, Orange, Red, Purple, Brown, Black, White, Grey.
Hard colors to obtain through breeding methods Orange, Red, Black, White.