I did a couple creative liberties so they looked more appealing: I copied Snake and made Princess Peach's sprite the same as Mario because the original was too small as well as altering Luigi's color palette to fit his modern look.
Otherwise they follow the same restrictions as their NES originals. | 
Very nice sprites, and I apreciate the detail that Mario and Luigi's sprites, who would appear on both blue and black backgrounds in-game, doesn't use any black/transparency in the sprites themselves.