Making the cartridge a different color is the kind of gimmick that just makes new games seem all that more special. Of course, there were times that maybe it didn't quite work out the way it was supposed to (Acclaim's red Maximum Carnage 16-bit game, anyone?), but for the most part, it works.
Nintendo's original NES Zelda games had the gold-colored carts, and for the latest incarnation of the series, it may be bringing that tradition back.
Now if that doesn't get your mouth watering, what will?