After great deliberation regarding colour and should I change it as the wheels were tatty I went for it and decided that a few shades darker would be good. I wasn't going to change but decided that the only important thing was the quality of finish rather than being the original colour (original colour was a problem to match precisely also) and the fact that my wheels had been touched up in the past.
Anyhow, I went to The Wheel Specialist and chose a colour called Gunmetal. Here's the result, which I'm very happy with! Comments welcome...