For the silver-gray metallic paint on the face of your AMG wheels, it's usually a custom finish specific to AMG models. You can find the exact paint code in your car’s manual or on the door jamb sticker. To fix the curb rash, I'd recommend sanding the area lightly, cleaning it thoroughly, and using a wheel primer before applying the paint. For the best result, it might be worth having a professional handle the repair, so you get that flawless finish.
One of the main issues with DIY wheel-paint touch-up is that normal body paints don't survive very long on wheels due to the extremely harsh environment ... such as the corrosive brake-pad dust and the high-speed dust/sand "blasting." Good wheel re-finishers use an oven-cured paint (or a powder coating), but that's not practical for most DIYers.
If you're lucky enough that there's a color match, I've found that the POR-15 Engine Enamel stands up pretty well, but it's not very easy to apply.
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
