Its kind of interesting, this question. I am trying to build some of the vehicle we had in our Engineer Company back in1967 68 in Can Tho RVN, and the OD color keeps coming up in my mind. Seems to me I remember the OD on our trucks and jeeps being a deeper, i.e., darker greenish color than the Mohawks stationed on our airfield. In addition, the C-7 Caribou's seemed to be a different OD altogether, but they all "worked", if you get my meaning. The colors also varied by the exposure to the tropical sun, and just how industrious the painter was when mixing the paint. I have color slides and pictures I took way back then, and I swear to you that no two look the same. . .it all depends on the angle of the sun, the speed of the film and the phase of the moon.
The entire thing is a toss up, it seems to me, and the rivet counters who insist that "this is the only true color" are just mistaken or fooling themselves. In the real world of Vietnam, the colors seemed to be as varied as the GI's who applied them.
Just my $0.02.