Why does Superman wear his underwear on top of his clothes?

Why does Superman wear his underwear on top of his clothes?:

Superheroes are a strange breed, often doing things we mortals don't understand. Why does Superman wear his unmentionables on top of his clothes? Hey, man, who the heck knows!

OK, but why does the Man of Steel dress like an '80s aerobics instructor? If we had to hazard a guess, we'd say it's for aesthetics and nothing more. Without the red trunks, he'd look like a male ballerina in blue pantyhose. And not even Superman could pull off that look.