It's not as easy as you think. The OE bulbs are not green they are clear. The gauge faces have a film on the back that cause instruments to appear green when illuminated. Adding a blue/red/purple bulb will not produce the exact color illumination. I tried to do red myself and it looked more like orange. To do it right you would want to take the cluster apart and carefully remove the film from the areas that allow the light to pass through (not easy). I know that aftermarket gauge face kits have no film, so illumination with any color bulbs produces positive results. Just changing the bulb color may not give you the effect you're looking for.
