If you are talking about Ralley II wheels, good luck. I have been at shows and seen five different colors of the gray and five different owners saying that theirs is the right one and the reasons why.
Having said that when I did mine I used Dupli-Color HWP101 Silver (the silver is really a pretty easy match) and the Dupli-Color HWP102 Graphite for the grey. I am very happy with the relults.
A few years back I ordered "Ralley II Wheel Paint" from one of the bigger suppliers of our hobby thinking that I would be getting the real thing. The paint came with a disclaimer stating that the charcoal paint they sold was darker than the original wheel color. They were right.