I agree with Bianchigirll. Aluminum nipples are corrosion prone no matter what color they are. If you ride in wet and/or salty conditions they will corrode. Brass nipples are stronger, more corrosion resistant and do less damage when they corrode than aluminum.
Good quality spokes (DT, Wheelsmith, etc.) are all stainless steel these days so corrosion isn't a problem no matter what color they are.