Nice subjects B. Huber
I'm pretty sure Büchner's plane was standard factory finish. I don't believe I've ever seen a production D.VII with anything else but printed fabric.
I'm pretty sure this plane, like all the others from Jasta 13, would have had 4 or 5 color printed fabric all around. Büchner's plane is almost certainly covered with 5 color fabric. It also light (probably blue) rib tapes and probably the same solid color wing edging too, not cut from printed fabric. They could have been pink and not blue though.
It looks like his plane had white walls! Definitely not something you see on war time D.VIIs but they sure look like white walls rather than dried mud or darker tread area.
The only photo I've seen that shows the horizontal tale shows that it was looking dark.
I'm pretty sure standard Jasta 13 markings were the same blue as the fuselage for the horizontal tales.
The green used for Jasta 13 looks very dark in the photos, which might not mean it was dark of course. But I'd be willing to bet that green was the standard OAW factory green.
One of the RGB quotes I have is 30/69/58 but it might have been more olive colored.
No matter the shade the all the struts were painted the same dark color as the nose.
The standard Jasta 13 blue was more dark than you have here, however, Büchner's plane was lighter than the other in the Jasta so you guess is as good as any others.
It looks like your colors are largely based on other artist's interpretations, but maybe give some thought to that green color. I doubt it was that light or bright as most artists have shown it. I have no idea where the idea of the Jasta 13 creamy green or bright green idea comes from but some of the earliest illustrious of Jasta colors show it and other artists repeated it with looking at that very dark color shown in the photos. Unless it is very yellow in color, it probably was very dark and not cause by orthochromatic film.
Some interesting reading about Büchner's plane along with most of the known photos-
Karl Schlegels Marking - Hopefully some useful Info - Page 2
Plus you'll need this one-
On your Dr.I, watch your interplane struts. They were not airfoil sectioned, they were flat slabs of wood. Check out these photos-
You might want to take a look at this-
Camouflage & Markings: Fokker Dr. I Aces
(The last section is about the Jacobs' devil head plane)
There is some debate about the flames across the fuselage reaching the front of the plane. It can't be see in the photos and might not have been there.