Yes, and that's why I said it's a brown with a green hue

Mainly because the standard US Army OD proved to be too light for use on aircraft. But this has caused confusion among enthousiasts and modellers since then, many of whom weren't (aren't) aware of there being multiple shades. It's not helped either by the postwar standard(s) being lighter than the original one, and the gloss and matt versions of those differing as well even though they weren't supposed to.

Steve Zaloga wrote a very good article about OD and the myths surrounding it.