Sorry mate, and I know it's a pain in the arse, but the centers HAVE to be painted black as in those pictures.
I've seen wheels, such as on my AX GT, that have been completely painted silver when they should have black sections too, and they just look so wrong, obviously painted, and pitifully shite, as though the owner just couldn't be arsed finishing the job of properly.
Do it properly and it'll look absolutely ace.
On saying all that, I still don't remember the GT having those wheels in the first place tbh.