[...you are the most laid-back person he has ever met. Gangrel sighs in defeat and rests a hand on his hip.]

Tomes. Dark Mages can use any tomes, but they're also able to decipher and use dark magic tomes, which most people can't use. I haven't seen any of those around here, so don't start thinking you'll be able to cast spells just because you're wearing the outfit.