Mmmh, I wonder, why specific blue or green?
If you're afraid of the light getting mixed up with gun flashes you should choose blue, when following bloodstains also get blue, in other cases I would pick green.
For myself, I chose red: it doesn't destroy your night sight/night vision and it is bright enough to walk trough a dark forest. When in need of reading a map I have planned my route before and therefore now any dangers. Beside that, on maps in the Netherlands the contour and warning signs are brown-red and light up grey under the A2-red light. So for me red works. And for warning cars (I often walk beside countryroads) a single flash of red gets most cardrivers cautious enought and they drive often by with no more then 10-15 miles. If they don't slow down, jump in the ditch beside the road or you might end up in it anyway. /ubbthreads/images/graemlins/sick.gif
What is the reason for choosing between green or blue?