You got me there harold. I don't use vallejo for my vehicles, only really for figures, and i only build post war British armour. But, its its an army vehicle, the col,ours would be the same. For the RAF, i believe there vehicles were blue/grey in the UK but camoflaged when deployed over seas.
This link might be of some use, its just a case of trying to find the right vallejo colours.
https://www.mafva.org/british-vehicle-camouflage-1939-45/?v=79cba1185463