A black vinyl wrap on the roof would look awesome on a white or gray car. You should do it. There really aren't any cons. If you don't like it, it can be peeled off.
2011 X5 xDrive 35d Red/Black: ZCW, ZPP, ZRC, ZTP, 300, 386, 496, 4AB, 6FL, Combox, LED Coronas. 04/11 Production