I recently picked up a Petzl Tikka XP headlamp, and the accessory filter set (red, green, blue). I've heard that green and red don't adversely affect pupil dilation as much, and know that when trying to pick nightcrawlers/worms red is good because they don't pick it up. What situations are the colors best for?

I believe Red is generally considered the best, but Green has become popular as it is a better compromise when using military night vision technology, which is becoming more common today.

Personally I'd say red with the naked eye. I haven't used the NV gear, but it is said (here and elsewhere) that green is better with it. But it can even be down to the person using it. Some have more sensitive receptors in different color ranges. I'd say go try them both, use stop watch and note recovery time in the same area to "I can see again" all the way up to "fully make out detail" night vision.

I don't think this is one anyone can answer for you, although generally Red is considered the best for naked eye recovery even by the military (unless they've updated their testing) for most people. YMMV of course. <img src="/images/graemlins/smile.gif" alt="" />

IIRC, red is to preserve night vision, green originally would show a blood trail better in the dark (as well as NVG use, stated above) and blue (flashing) distinguishes you from ground fire (which is usually white).

Soviet made tracer ammunition is green, US is red.

Yes, and non-tracer ammunition is seen as a white flash. So blue means "pick me up, I am here and not over there shooting at you" with white, red, or green.

Also, different color filters can be used as pre-arranged messages. Two green flashes mean something, three red flashes mean something else. I also seem to recall that reflected red light cannot be seen as far as other colors.

Both work realitivly well to preserve night vision. I personally like green. I have found that green light provides better illlumination for hiking and for reading maps. I have also found that a lower level of green light to be useable than red.

Green is also the color of light that is seen easiest by the human eye, which is why NVD displays are in green.