Where's the data? I'd like to read that study. Being a retired investigator, I have suspicions as to the applicability of the human eye's perception of green, in this context.
Nature is full of wide range of greens. So what better color to blend in than one of those shades? Even on a rock outcropping, from afar a green object can easily be mistaken as a tree/bush/brush or something organic to the landscape.
I did a little study of my own a few years ago with a photograph taken above of about 8 tents of different colors, including a few shades of green, all pitched in a distant field. I individually asked 7 people to tell me which tent they had the hardest time spotting; which one stood out the least. It was the dark green tent which drew 5 votes, followed by the slightly lighter green tent with 2. Neither matched the field color perfectly but no one picked the gray, white, orange, tan, etc. tents. My vote was on the darker green tent but I didn't count mine. 2 people were with me when I took the image and they mirrored the data. I could probably dig that photo up, amongst my 100k+ images.