If you can change the colour, a dark silver/light grey would work.
I have matt graphite rims on the 997 and they look black against the white. They're a bit too dark. I've got matt black rims on the other [(grey) car, and they look crap. I might have them painted yellow. We've got gunmetal rims on the other-other car, and they look really good against the thunder gray paint. Hope this helps.