Had this problem on my Fiat Coupe, it had titanium coloured alloys ( check the site for an idea of the colour ) that nobody could give me a paint code for, most annoying, anyway a trip to my local chipsaway ( www.chipsaway.co.uk ) solved it they took the wheel off and did a colour match by eye touched the wheel up, relaquered the wheel and it looked perfect, colour was identical to the rest, cost £40 to get the wheel done with the colour match but its cheaper without if you have a standard silver type alloy (£30) , they would also do a deal if you had the lot done.
Cheers