1. Metallic Tones: Ok, so this isn't exactly a color, but metallics are really hot right now. To get that really shiny metallic look you'll want to consider dresses made of iridescent taffeta (there are loads).
2. Blue: Blue prom dresses are shaping up to be massive in 2012. Prom being formal, you may wish to go with a darker blue which lends itself better to formal events, but most blues are going to look good.
3. Orange: I know that orange wouldn't be most girls' first choice when it comes to their choice of color from all the 2012 prom dresses available, but did you know that orange has been voted 'color of the year' by the color experts? If you're worried of looking like a giant fruit, how about choosing burnt orange or ochre colors?
4. Nude: Nude was big last year and it still is! It's also good, as nude colors suit everyone and are rather appealing.
2012 prom dresses in trendy colors may not be promoted as heavily then; therefore if you take time to dig for them (which many girls won't) you'll have more chance of turning up in a unique dress.
