Ooooh, I dont know, I like the idea of yellow, but to be honest, blue, would be better, depends of you want it to clash or not, but I'd say that you have gone all out of your way to get the wheels with the Blue rims, that you would probably spoil that with different coloured calipers...
Black would be too Plain I wouldn't even consider it, and red or yellow, would be really out of place as theres no other red or yellow on the car... Yellow less so perhaps because of the stickers, but then teh stickers look a little out of place as the only yellow on the car just now...
So yeah... Lots of random mumblings later, and it would have to be Blue!