Considering that their current methods of creating custom keycaps consists of either laser engraving or etching, and not actually molding plastic, I would not expect this to happen (ever).

You can get backlight keys in different colors through sellers that offer Ducky Keyboard brand backlight keys. You can find those in all sorts of colors and ISO/US formats, but nothing more than that unless you join some type of group buy through Geekhack.org or Deskthority.net where you can find all sorts of 'one-off' sets custom keycaps.