system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the human eye colour generally Brown, Blue and other similar variations. Why no bright green, purple, black or orange?
gpt
Eyecolor is determained by the amount of melanin in the iris. Melanin is a darkish pigment that helps protext the skin and eyes by blocking damaging UV rays. 

The color comes from how light is refracted in your eyeball with the melanin. Blue eyes have the least amount, leading to the color blue being reflected mostly, in a processes similar to how the sky is blue. 

More melaanin causes more brown tones, leading to green with a little more, and greys and growns with other amounts. 

The way light reflects with this pigment doesn't allow for purple or other colors to show.