. You also mention the possibility of higher brightness vs. other LEDs in a given model - what specifically do you mean? Are Blue LEDs more efficient at a given brightness? Operate at a lower temp?
Blue LEDs are the most efficient (watts out/watts in) LEDs by far, I suspect this because blue is what is used in white phosphor LEDs, and there's a big push to make the white more efficient. Even though the eye's sensitivity for blue is fairly low compared to a lot of the other colors, this is made up for by the fact that the LEDs are so power efficient compared to other single-color emitters. By shifting the spectrum slightly toward blue/green, it's possible to make very bright LEDs because they preserve the efficiency of the "blue" LEDs, but the eye is a lot more senstive to cyan.
Green LEDs are surpisingly inefficient (power out/power in -- producing fewer lumens than red or blue in many cases, even though the eye's sensitivity peaks sharply in the green. I suspect at this point it would actually be more efficient to use a blue LED plus a phosphor and green filter to produce green, than to actually use a green LED.
In terms of separate colors, I think that blue is the most useless for my use.
It's supposedly useful for following blood trails from wounded game, or people if that's your thing.
green is more useful in the given example of tracking blood -- as grass/brush will reflect it, but red blood will not, so it will generate a stark contrast, even with low illumination. Green is also focused sharpest on the retina of any color, blue is the least focused.
As for the issue of looking for things that fluoresce, near-UV would be better, it can cause a wider variety of things to fluoresce (such as paper, cotton shirts, money) and the
only visible light in that case will be caused by fluorescence -- blue light may caause things to fluoresce, but reflected blue will make it will harder to see.
In terms of night vision preservation, red is by far the best -- as it's possible to read by it, yet not disrupt night vision at all. Blue is the worst, as not only do the cones of the eye have poor sensitivity to it (can't see as well with it), that's where the rods have their peak sensitivity, so enough blue to be useful will immediately wipe out night vision.
I remember reading somewhere that blue light annoys the eyes. So if you're feeling sleepy, shine some blue L.E.D.s at yourself. Anecdotally, it's worked on me and my friends.
The sun produces strong cool white output with a lot of blue in it. The moon on the other hand does not reflect blue very well, so presence of blue is the way your body can detect if it's daytime or nighttime. Artificially producing a lot of blue light is a way of "tricking" your body into thinking that it's daytime.
