I poked around this subject a bit, earlier in the year, and really couldn't come up with any official specifications or anything.
The pics that I found of older US vehicles in Belgian service, looked to be in either a faded US "olive" vehicle color or a slightly more chalky, washed out version of that color. I'm guessing that the photos mostly dated to the late 1960s and or early 1970s, though a few stated that they were from the 1970s. The color leaned more toward a slightly yellow olive, rather than a darker, more brown olive.
For this, I would start (its what I will use, when I finally work on some Belgians next year) with a base color of Vallejo 887 US Olive Drab (it use to be called Brown Violet, but my more recent bottles have the US OD name on them). The lighter, faded color could be achieved with a mix for the base coat, and possibly through shading/weathering. Depends on your preference and painting style.
Again, I can't say what is "correct", but the greatest frequency of what I saw in photographs of in service vehicles seemed to be a faded olive color.
Hope this might be of some help. best of luck with your project, and please share your work if you can. I'd love to see what you come up with.
adds APCs to his Israeli forces.
