I also have an RS, I just got hold of some Audi RS4 wheels for winter wheels and going to spray them myself, I have also had the Omanyts on my car and personally I love the silver on silver look, just nice brilliant mint silver on a silver car in my eyes looks spot on!
These will be going silver I'm sure, or a nice LIGHt Anthracite grey colour like this -
Just ever so slightly darker then silver, but still prefer silver :D don't dig black wheels on silver (sorry!)
Personal choice, remember it's your car!