Traditional etiquette holds that yes, this is rude; on the other hand, many people do it.
I guess if the outfit doesn't look funeral-y (and many black outfits don't), it's okay; but if you look like a widow, it's not. Even then, it's very subjective. I guess one's actual manner while wearing the outfit and any accessories, makeup, hairdo, etc. would also be factors. For example, a black strapless dress with shiny high heels and flashy jewelry coupled with a "let's party!" attitude wouldn't look funeral-y.