Andy, I've just had a look at more references and pics (and PM'd Paul), where the change to 72 overall upper surface is evident throughout, the earliest photo being from early 1941 (albeit Luftwaffe, at Brest), with others from 1943 to 1945, in various theatres and locations, with Luftwaffe, KM, and other axis users. Profiles covering these periods also show the single upper-surface colour.
I'm a bit knackered at the moment (another painful 40+ hours without sleep), so can't think clearly, but I'm fairly sure that somewhere I have a more detailed reference, specifically for shipboard aircraft. I'm off to bed now, but if I can remember, when I eventually regain consciousness tomorrow, I'll have a search for it.