There have been already a couple of threads on the issue. The latest one seems to be
this one.
Unless you have specific uses for a certain color, go with white (explanation see
here). The rest of the Q&A's on Quickbeam's
flashlightreview page are also quite helpful.
Mine is white. My second choice would be red (nightvision preservation).
Personally, I do not see much use for other colors (except coolness/showing off). Pilots probably get the most use out of yellow-green ones, since their maps are either monochromatic or optimized for this color.