pert:
Well diffused RGB LEDs can give you any color you like. Otherwise you could try shining white LEDs through a transparent colored material such as lighting gels (which are available in a huge array of colors) or transparent paint (you'll have to test to determine if it's suitable for applying to LEDs).
I've tried a few transparent paints, but it wasn't working for me. Too messy and difficult to mix colors. I chose to go the arduino route so I could learn some code.