It is recognized that black trousers are slim. However, it also depends on what style and clothes you wear.

Generally speaking, wearing black pants has a very good slimming effect.

I just made a simple picture. In the same background, is black thinner than pink? But in fact, their area is the same. So, do you think the color matching is amazing?

So wearing black pants will be thinner and more versatile than wearing pink pants.