First of all, any color is fine.

Second of all, "black tie" for women is somewhat nebulous and usually translates to "floor-length."

Ergo, wear what you like and what flatters you best, as long as it's not a floor-length dress - and frankly, even if it is, that's fine too. Anyone looking at you will only notice how great you look, not if you happen not to match.

(The foregoing courtesy of my wife and mother-in-law)