I used a black base coat to save on paint costs, but it served another useful purpose. For weathering or any future damage any chips would likely be red primer or black. The final top coat was standard NATO olive drab, which has a slightly yellowy tinge and I luckily found somewhere that sold large sized cans in the UK.
The paint issues I mentioned in an earlier step were to do with the paint cracking and peeling up wherever it covered the wall filler I had used. Once sanded back and resprayed it actually helped to make the vehicle look a bit more worn.