Well, I fear I have to add something to this idea of a two coloured upper wing of Hitschler´s Pfalz DIII /D IIIa
You will find a real good photo of this Plane under:
Flugzeugforum
Unfortunately it’s only in German language and you have to be registered to see the photos, but under “Forum-Luftfahrzeuge-Props-Alte Fotos aus der Doppeldecker-Ära-page 4”
you find an excellent, if not the original photo of Hitschler´s plane as shown in the Osprey book.
The photo is presented by "John Silver" in the forum).
Compared to the print in the Osprey book, where it is indeed possible to see a colour demarcation line on the top wing, this picture does not show any.
What you can see is that around the top wing radiator the colour is a little bit lighter then on the rest of the wing, but that’s it. The lower wing and the elevator seem to have the same grey tone as the upper wing.
The demarcation of the red/blue on the fuselage is clearly visible.
I really don’t think that this photo gives a good reason to postulate a light blue / dark blue wing configuration.
If someone wants to be on the save side, well, he may assume that the wings and elevator should be in JG 2/Jasta 18 blue.
If you still see a colour demarcation on the top wing, I cannot help to think that the wings and elevator was in the usual two-coloured mauve/green. Maybe in the sometimes-found mauve left, green right wing configuration of some Albatrosses.
Only my 2 cents.
I’m awful sorry my source is so hard to reproduce on the pc, but maybe someone of the forumites finds an easier way to get access to this picture….
Thomas