Tony, the short answer is Khaki Green No.3, which was adopted as standard in August 1940 and remained so throughout WW2. However it was darkened in late '42 so there were actually TWO colours, commonly referred to as pre-42 KG3 and post-42 KG3. Also it acquired a satin finish after July '44 which can be seen on some new vehicle photos:
General Routine Orders No. 278. 28th July 1944. Painting of MT Vehicles
Vehicles will, in future, be painted in a single colour, namely Khaki Green No. 3, and will be finished in “egg-shell” in lieu of existing “matt” finish.
