system
Given the following post, respond as if you're commenting on Reddit:
human
Why is cloth darker when it gets wet?
gpt
In dry cloth, light gets scattered and reflected mainly by the particles on the surface.  In wet cloth, some of the light gets carried into the material by the water, acting a bit like fiber optics.  The end result is that less light gets reflected or scattered back.

Consequently, this same phenomenon is why you can see through wet paper better than dry paper.