Color Matched Bumpers?

[njmaxpayne]

i'm also doing the roll pan first!

 

[Mr.Jack]

I also have the crome bumpers, and want to make them black. But how should I do it? Do they have to be sandblasted first or something? And what kind of spraypaint should I use?
I also want to paint the lower front air deflector which is gray on all cars. I do not understand why GM chose to have them gray on all models.

Bjorn
Norway