Interesting, I did a quick search as well once you commented. It seems the RAF blue was a pre-'41 color and then applied again post WWII in '46. WWII RAF jeeps from '41 until '46 were left in standard OD Green as delivered, or painted overall sand for N. Africa service.
This is how a wartime Willys MB would have been painted and marked.


This RAF jeep from WWII seems to only have the roundel on the side and no lettering on the hood. The color looks OD to me, but it is hard to tell in a B&W photo.

Additionally, British Army jeeps had an "M" serial number, not a "U.S.A." serial number, like below.

