Women can wear sweeping floor-length evening gowns. No cocktail dresses or short dresses and light and bright colors are not preferred. Dark neutrals and jewel tones are preferred. It is safe to assume that black tie means fancy, and you really can't be too over-dressed.
No, a black-tie dress code doesn't refer to the color of your dress. You should go with a more subdued or evening-appropriate color, sure, but your evening dress at a black-tie wedding doesn't have to be black.
A tuxedo, or a dark suit with a white or blue shirt, a dark, simple tie or bow tie, dark socks, and dark shoes. The idea of this outfit is to approximate the formality of a tuxedo without actually being a tuxedo. Dark Navy or Charcoal Suits also fit this dress code