I think is a reasonable choice, I did the same for my 15mm Main force to have a visual differentiation. Ok now I will not do that for several reasons, including the fact that it was quite unusual to encounter mixed units. I have read several comments that the 'export khaki' was quite awful and no one PAVN of NLF was really happy with them, plus they stood out in several backgrounds. By 1967 almost everyone was PAVN, local recruiting had dried up in 66 and people from the North exerted more and more control. Plus by 66 the politburo has moved to full scale conventional war and PAVN types were coming to teach everyone a lesson.
Still the tanks looks weird and more dressed for desert. I know that on the concord book on the Vietnam Armor at least one PT-76, is painted khaki, but every account I read was that they were green. Bear in mind that the Pt-76 depicted is based on the one recovered at Ben Het, all suffered massive internal explosion after bing hit by 90mm fire or mines so I think the colours could have changed a little.
Said that I like them quite a lot, at the moment my micro Vietnam is 6mm with 3mm helos and air, but you are putting weird idea in my rotten brain.