Press photo from operation Doomsday Norway 1945,an Airborne despatch rider on a G3L.Airborne vehicles should have the C number painted in light blue,but its hard to tell if this was done on black and white photos. 
Good point Jan, but I don't think so. Unless done at unit level. Since I expect that the census numbers where all put on at the factory, would they have been aware of what units they were being supplied to?
This well known picture which I think was one of a series which was taken during training just prior to D Day (part of 'Exercise Smash') seems to have a white census number.
Coupled with this picture which I am assured by a very reliable source, is all original.
I guess also, lots of vehicles which were air portable, where not necessarily with Airborne Forces? Ron
email (option): ronpier@talk21.com