Is it rude to ask guests to wear certain colors to your wedding?

I do not think that this request would be rude, however it's not what you ask it's how you ask. If you can make this request in a soft, warm and gentle manner. ( "Black and White evening attire will be appreciated' or "Black and white attire would be optional".) something similar to that. That way you are throwing it out there but not being too demanding at the same time and you'll be surprise how cooperative people will be and people tend to have a more softer side with weddings and even more especially "the bride". So please, if that's what you want give it a whirl, remember it's your DAY, you are spending thousands and thousands of dollars to make this day special, but remember do not DEMAND it but do put it out there about your color preferences.