I keep a white Photon II in my pocket every day. It's real useful for "daily" lighting needs (finding the hole for a key at night, looking in dark corners, emergency light when the lights go out, etc). I've got a blue Photon I on my key ring...it does pretty good, casting a good wide beam but having some color distortion. My only red Photon II is in a kit that goes with me when I'm in the woods.

I don't think you can go wrong by buying several...try some different colors. You'll always find a place to keep them and they can come in pretty handy at times.