Costumes are one important manifestation of their personality and usually it has features which serve a specific purpose.

For example Batman and Superman.

They are known for team-up; however you don't expect Superman to be flying around all dark, because it's just not his style. Batman on another hand needs a dark custume to hide himself in the shadows.

However it's normal that other organizations, like the Green Lantern Corps keep similar uniforms, as they are more, let's say, "official" organization.