Hey Guys I thought I would share this tech with you. It could save some people some significant money and help change the look of your wheels.
I bought my B7 S4 from a guy that lived in california who had put 19" wheels on the car and sold the stock rims. He then moved to chicago and discovered he needed winter tires and wheels. So he bought A4 wheels.
I didnt like how the A4 wheels looked on the car (being white) so I did some research and decided to paint them. The process is described below.

1. Sand stock wheel wherever you want paint to stick. You dont have to remove all the paint but just make it dull and smooth. I used emery cloth. You don't have to go real fine with the paper unless you want a really glossy finish. (I didnt).

2. Mask all areas you dont want to get paint on. For the tire I used cut up beer cases and stuck them in between the wheel and tire.

3. Paint the wheels with Duplicolor wheel paint. I applied 3 coats of black paint, then removed the masking (once dry) then applied two coats of clear coat.

Easy as that. Took me about 3-4hrs total.

Sanding all the areas is the most important step as the paint will not stick to the wheel otherwise.
Hope this helps.