Why are southern white rhino's gray?

Rhinos are gray and not purple because a lot of light is being absorbed by the skin, and only some is being reflected back towards our eyes, making the rhino look gray. It also has to do with skin pigmentation. It is just the type of pigmentation found in all rhinos. Rhinos could be purple if their skin pigmentation changed to be that way, but it didn't, so rhinos are gray.