system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why fabrics get darker when wet?

I've always wondered why fabrics are darker/ more vibrant when wet? Is it literally (no pun intended) the saturation of the color increasing? Or perhaps a refraction of light? ELI5 please and thanks!
gpt
Here's an easy experiment.  Place a drop of water on a paper towel.  Notice how the wet spot looks dark?  Now hold that paper towel up between you and a source of light.  Notice how the wet spot looks bright?

The water increases the ability of fabric (or a paper towel) to transmit light, which means there's less light to be reflected back toward you.  So the wet spot will look lighter or darker, depending on whether you and the source of light are on the same side of the fabric, or not.