There are several shades of green that these trucks were painted in, depending on branch of service, year of service (era you are trying to replicate) and general color (camo, semi-gloss OD, etc). Are you wanting CARC style paint? Just a simulated finish?
Maybe a bit more information about your truck and what you're trying to do with it.
I did a google for "Military Paint" and got several hundred interesting hits. There's also a lot of info in the forums here...a quick search will turn up a bunch of treasures, especially on prep, primer, and of course the paint itself.
Hope that helps...