I've been told that Y/G is a NV Compatible color, and is also a good color for working with maps at night... supposedly it's more like white, in that colors appear more natural under it than blue or red, due to the fact maps don't use that color on them. Supposedly it's also a very bright color to night adapted eyes without making them not night adapted.
I can tell you from my 1 week worth of playing with my Kroma's (have both models still can't decide which I like better, but leaning towards MilSpec) that the Y/G is a great color at night... I haven't used it with fully night adapted eyes, however I've noticed if I wake up in the middle of the night it's plenty of light even inside the house, to see what I'm doing, and walk to the bathroom, etc... it's very dim in comparison to the red, and blue, which means less visible to others, less likely to ruin night adapted vision, etc.
I was told that NV Gear does not see Green or Y/G colors so that if you were to look past a buddies nvgear on his rifle, it wouldn't mess your unit up. I can tell you from trying it out, that at least on my Gen1 Unit this is not true... HOWEVER it is NOT very bright to the Gen1.
The Y/G appears through the Gen1 about as bright as the IR LED's (a bit more focused light) the Red/Blue Leds are much brighter through the unit. So I can say from experience that it may still see it, however it is definitely not as bright, of course it's not as bright to my eyes either. So it is VERY useful when working with NV gear, as it will not appear much brighter to your buddies than other IR sources around (low intensity IR sources, not high intensity) but will give you visible light to read a map, etc.
It is for sure not very much light, the Y/G A2's put out more light, however it's about the perfect amount of light to read a map, look inside a bag, and even see a few feet in front of you when walking.
According to resent reading I've been doing about human low-light vision, The part of the human eye responsible for seeing in low-light is most sensitive to blue-green so Y/G is fairly close to that color. There's some controversy about good colors at night, but the leading story I'm now hearing is that Turquoise (Blue/Green) is the best color for working at night, as it will not mess up night adapted vision as bad, but will give you what appears to be a brighter light source given the same amount of light, but that even white if used at low enough levels will not mess up your low-light vision as bad as a bright red source (traditional color of choice for night preserving vision).