It’s not a new problem either. I have a copy of all the A&A games from the Milton Bradley edition onward, and they add up to about eight different shades of US infantry pieces. The MB brownish-green ones and the Marine pieces from the original Pacific game have good reasons for deviating from the medium green which became standard in the original Europe game, but I find all the other shade variations annoying. At least the equipment pieces have been a lot more consistent.
I don’t know much about the process used to manufacture injection-molded plastic pieces, but it’s possible that green is (for some reason) a tricky colour to produce in a consistent shade. An added problem is that green is notorious for looking different in different lighting conditions: in daylight (which is bluish), incandescent light (which is reddish) and fluorescent light (which is greenish). Some of my American troop sculpts look utterly identical under some lighting conditions, but completely different in others.