Here is a link with a little info on painting the gauge trim.
There is an old thread with a complete write-up and pics, but I can`t find it now.
The best results will be obtained by taping the main part of the gauge off from the trim rings. Prying the rings off will end up with "ripples" when it is reinstalled.
I recall someone mentioning to use a flat black paint to cut down on glare that is common from the polished trim rings.