Remember that mobiles over the crib should help soothe your baby, not stimulate. Save the black and white mobiles for over the changing table - black and white graphics (for newborns up to 5 months in particular) will keep them too entertained to fall asleep! Luckily, you can still be mod without resorting to a neutral color palette. Here are some great modern mobiles to get you started on your search - all of them are just one of many styles available from that brand, so click around!
(Images: as linked above)