I'd go with seperates. Cause what superhero retail store would sell underwear on the outside of their tights like that?! LOL Plus, they're tights, unless Superman wants you to see his jewels, he had to find a way to cover them. Wala! The underwear!
I also agree with the laundry argument. But an easy way around this would to just wash them in COLD water ;)
lol....so supes is just the biggest fashio victim ever!!!! *giggle* and supes doesn't freeze.-.so he could use cold water--or maybe the suit washes itself. heeee.