UCP/ABU "foliage green" is not a good camo color. It only works best in a very particular setting. Frosty grass.

Neither color really works on their own.

I always assumed the "foliage" in question was desert foliage like sagebrush or the like. A number of desert plants are covered in protective trichomes and appear a silvery gray. Of course dramatically different than verdant foliage pretty much anywhere else.