Why are Kuwabara and Yusuke's uniforms different from other students?

Question

In YuYu Hakusho its possible to see that Yusuke wears a green uniform and Kuwabara a light blue uniform. Nobody else wears uniforms like that in their school.

Is there an explanation?

Answer 1

This is probably the case of Transfer Student Uniforms as described on Tv Tropes:

New Transfer Students in places where school uniforms are a cultural default setting often wear their old ones until the school can provide them with a new one. In fiction, this shows the newcomer or outsider. When they get the current school uniform, this indicates they've been assimilated. If the student is meant to be a Fish out of Water, they will keep their old uniform throughout the series. In Japanese media, even rebels don't choose to abandon uniforms entirely; in American media they will do this even if the new school doesn't have uniforms. Compare the Non-Uniform Uniform.

And on that same page, it describes the incident in Yu Yu Hakusho (note Kuwabara's case):

Yusuke from YuYu Hakusho distinct green uniform annoys the faculty, since while technically acceptable he wears it just to stand out. Even Kuwabara wears a slightly different shade of blue than the standard uniform. This is anime-only, though; manga color images usually have Kuwabara and Yusuke's uniforms matching, even if the colors aren't always consistent, unless the artist was color-coding them. Keiko calls Yusuke on his green uniform in the dub, but the original doesn't really mention it.

It happens in a lot of other anime/manga as well, commonly enough to be considered a well known trope.