Why do humans have brown skin?

Question

I’m not asking about dark or light. I’m asking why not shades of blue or green?

Bonus question: hypothetically, what factors could lead to other skin colors, like the aliens in avatar?

In: 18

Answer 1

To get other skin colours you would need a different coloured pigment other than melanin. The gene for a different coloured pigment is unlikely to turn up spontaneously. So we could start growing algae on our skin like sloths (green pigment in algae is chlorophyll) or genetically engineer ourselves to produce different coloured pigments in our skin. Like green fluorescent protein. Then we could glow in the dark too!