As i have already said filing of the green backing is the only way to do this mod correctly, use a womans nail file for this as i found this easier (just dont tell the wife). Using colour LED`s even after filing of the green backing will still leave the light behind the dials patchy and lit up more in different places. You must use styling gel over the gauges and use your standard white bulbs to create a proper spread of light.
(styling gel is used by photographers and stage lighting peeps and is available on e-bay)
http://cgi.ebay.co.uk/LIGHTING-FILT...ec_LightingLEDsStrobes_RL&hash=item415199ee52