system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does wearing black make people seem slimmer?
gpt
Because black absorbs most light, rather than reflecting it like lighter colours, we can't see much detail in dark clothing.

When we see someone wearing a light coloured item of clothing, more light reflects: specifically, it reflects differently depending on the shape of the person - lots of shadows, different light levels etc.

What does this mean? Well, it means we see all their lumps and bumps and bits that stick out, because we can see the shadows created by those lumps and bumps more clearly.

With dark clothing, we can't see those imperfections as easily or clearly, so our brain assumes they're smaller/not there.

The same applies to some extent with the sides of the clothing - because the clothing is darker, there's no clear "shadow" as the body curves away. That means our body assumes the dark areas to the sides are all shadows at the side of the curve (rather than front of your body) and we "see" the person as "narrower" (or slimmer)