Colors mean lots of things... white could also mean marriage, ice & coldness, death, heat, brightness, smoke, & it can give the dance a dream-like quality. In Swan Lake the swans are white, yes, because swans are usually white. They are also not human and don't want to associate with humans. They are cold towards them, standoffish and ethereal -- the white shows them outside the world of man. I don't know about shaggy culottes... haven't seen that.
Sometimes costumers DO get carried away!
Red & Black together are very violent, aggressive colors. They're both hot colors, though black (like white) can also be cold. They're dynamic and usually meant to be frightening onstage. They're also masculine colors.
Pastels are friendly, happy and calm. A male dancer wearing blue will usually be partnered with a ballerina in blue, often in a lighter shade. When they are not partnered together during the dance, it often expresses harmony and community, though usually they'll come back together at the end. You can also follow a ballet by knowing that the main dancing pair will be in a slightly richer, slightly different costume from the rest of the company. They may be the only ones in a certain color... or they may be in color while the others are in black & white, or vice versa.
Because there is no speaking, these things have to communicated through other means... including color. Nationality, status, age, state of mind... these things are also represented through the cut & style of the costume. A character in distress, for example, will frequently wear a costume that appears torn.
Here's an interesting forum you may want to check out: Critical Dance
. I haven't read a lot there, but it seems to be a forum for dance set & design specialists... pretty interesting even when they're just griping.