Is there any reason melanin must be brown/black or pink/red?

I'm writing a story in which I want to represent different ethnicities of human. however, for various reasons, I want to avoid using the actual ethnicities that you find in humans on Earth. At one point skin colour is important, however and, while this is set on a fantasy world in which magic exists and I could therefore just have people look however they look and damn the explanation, I want to avoid that kind of thing as much as possible. What research I've been able to do says that there are two different types of melanin responsible for colouring (and a third type in the brain the function of which is unknown) - one which is black/brown, and one which is pink/red, and that these are found in different areas of the human body.



So the question is - is there any particular reason why melanin could not be of a different colour? Obviously, the brown/black pigmentation has a function in reducing UV absorption, which is a survival trait, but that shouldn't necessarily exclude other colours.