It's just a small wedge base bulb that you can get anywhere. The lens is clear, so the bulb provides the color. Take one out and bring it with you in the store and find something like it in the color you want. I think new they were some sort of green color, but I'm not sure, it was so long ago.
I've been using red for about ten years now-
Red or blue may be illegal where you live, but I've been pulled over by cops lots of times and they never bothered me about 'em.
Mark Griffin