system
Given the following post, respond as if you're commenting on Reddit:
human
My eyes change color. Why is this and what determines which color they change to?
gpt
Your eyes are probably blue, or grey. It has to do with angle, intensity and colour of light that passes through your iris. What happens is that colour of iris is created by its internal structure scattering light. 

Darker eyes have a "paint" which works like a paint - absorbing colours and reflecting only certain shades. Light eyes need to rely on their structure in order to be colourful, so they change depending on light.

Fun fact - the same rule that make your eyes blue, also make sky blue. It's called "Rayleigh scattering".