Its better to base a villains appearance on his profession, how wealthy/poor he is, how cultured he is, what culture he belongs, whether he likes functional outfits over theatric ones, etc... rather than simply based on his morality. Treat him like you would any other character rather than singling him out into his own little dressing room of evil. Unless dressing in something that has an evil appearance is plot important (IE: the story actually has a reason why he chooses that outfit over a normal one for his position) then he shouldn't dress any different than any other human being who previously was in those same circumstances.
To use a real life example, Louis XVI didn't dress in a Light Is Not Good
fashion because he was a greedy hypocritical arse and he wanted the world to know — He dressed that way because of his position, culture of origin, love for flashy outfits over functional ones, amount of wealth, cultural expectations his peers had about the French aristocracy, his own
expectations of how the french aristocracy should dress, etc etc...
Remember that an antagonist doesn't need to be visually recognizable as the bad guy from first the glance the reader has of him, so long as his actions, reputation, and/or words are showing his true nature.
edited 15th May '13 12:58:24 PM by SalmonPunch