If you are only giving or getting one Photon Micro-Light II, give the white one. Since they narrowed/brightened the beam, it is the most practical color. For example, if you are plugging a color coded wire into your computer or similar task, only the white will let you readily detect the color.
The other colors are useful and fun if you can get more than one, or have a special purpose in mind. The two attributes of other colors besides fun are longer battery life and preserving night vision. The preference depends on application. The yellow is fairly useful, long battery life and reasonably good beam, yet not too bad with your night vision. Red is very bright, long lasting, and other than the brightness aspect preserves night vision, but I just do not like viewing with red. I also recall complaints about having trouble seeing red (?) lines on maps.
The green now comes in a two versions I believe, one brighter with shorter battery life, and one with very long battery life. I have the latter, and perhaps it is a very old version, but I have never found it bright enough. I believe certain groups use green in preserving night vision for their applications. At the moment my green is not working because no matter how I reassemble it, it goes on to easy. It may be me, but I have not had this problem with any of my other lights.
The turquoise and blue are very pretty. Battery life is similar to the white, I believe.
The orange color is worth some comments. It seems good for getting up at night, not too shocking to the eye, and a little more pleasant to me, probably both from being up from red in the spectrum. Two problems though. It may not be one of the long battery life ones, it does not seem so to me, as I have not used it all that much, and it seems as if it would benefit from a battery change. I do not recall what the manufacturer claims for battery life. Further, at least mine has very pronounced rings which limit its usefulness.
Special purpose: Infrared and Ultra-Violet. The latter is new, expensive, and on my wish list, but I have no idea of the battery life and I recall that it only has the momentary on switch.
Caveats: I have not reviewed any of the recent offerings and they may have been changed. The narrow beam white has been out for at least a year and so it should normally be the one you would encounter in purchasing, but do not get the old one unless you have some special reason. If it has a bright, somewhat focused beam, you have the new one. My comments are all regarding the ones with the constant on switch, i.e. the II model, unless specified.
In sum if getting,
1 light = white
2 lights = white and yellow
3 lights = white , yellow, possibly red or your favorite color
4 lights = white, yellow, red, and your favorite color (or perhaps the extended battery life green if you find it bright enough)
