system
Given the following post, respond as if you're commenting on Reddit:
human
Why do fabrics and hair look darker when wet?
gpt
Short answer: because moisture (water) scatters light particles, so that more of it ends up getting absorbed/going through the material and less of it gets reflected back to your eyes.

EDIT: Fun fact - if you have a wet spot on a piece of fabric and there is a light source behind it, the spot will actually look *brighter* for the same reasons.