I'm afraid you are wrong, sir, for once.
Formal covers a multitude of sins. The instruction formal merely dictates that gentlemen must wear a suit and tie. Black tie is then the next stage, requiring a dinner suit and bow tie rather than, say, a lounge suit. Technically black tie doesn't dictate the colour of the tie, but only a terrible prole would wear a coloured or patterned bow tie. White tie is the highest of the high and means, well, a white tie and a jacket with tails, and as Ambrel pointed out, is really restricted to ambassadorial functions and universities with ideas above their station.
( the mighty badger Aphrodite, on a bar stool, by your side, Tue 25 Jan 2011, 16:43, Reply)