Hi, I too have struggled to find out. All I do know is that mine is a kind of pastel grey / bluey white that was painted over the VW L275 Light Beige at the Dormobile factory. I have got a Dormobile colour card that shows various colours they used at The Tile Kiln Lane Factory but there is no reference to which vehicles they were applied to and none of the colours look to match anyway!
Maybe you could remove something small (tailgate hinge cover) and get the colour matched by one of the clever paint people who use spectra thingamabobs!
If you or anyone else do go this route, give me a shout as I would be interested in getting some rattle cans made up
Cheers
Andy