system
Given the following post, respond as if you're commenting on Reddit:
human
How does eye color change?

I know that some people have eye colors that change noticeably and that children may have blue eyes that change color as they get older. How/why does this happen?

Edit: Also please answer kwagener's potential color changes "Mine go from dark brown to bright green depending on the mood I'm in"
gpt
It's not that the amount, or color of, pigment in the iris changes, but as the iris dilates and contracts, the pigment becomes concentrated or spread out, changing the perceived color. There are also differences in perceived color depending on the type and intensity of the light source. 

As for babies, some are born without the pigment fully developed, and it takes time for it to come in.