system
Given the following post, respond as if you're commenting on Reddit:
human
Why does hair come in just a few colors? And why these colors?

As the title says - why can we only have different shades of a few specific colors of naural hair and why can hair only have one of these particular colors and not, say, green?
gpt
Layman.

There are two major natural pigments found in hair. Eumelanin is black or brown. Pheomelanin yellow or red. Our hair colours are limited to what can be produced by mixing these two pigments in various quantities.

I can't say why we never evolved to produce another pigment (like a green pigment).