Hi Fellows,
To try to answer all the questions: Ed Ferko had von Buttlar's own photo album, which served as much of the basis for Ferko's excellent history of
Jasta 18 which appeared in his book
Fliegertruppe Nr. 2, which he self-published in 1986. This photo (below) came from von Buttlar's album:

This isn't the best print , but it will have to do. Ferko stated (in no unequivocal terms) that: "Lt. von Buttlar recorded beneath the smaller print (the one above), 'My Pfalz D.IIIa.' Five narrow white bands encircle the over-painted fuselage." It would seem that a mechanic is seated in the aircraft in this photo. The two photos I posted earlier, showing von Buttlar posing in front of and seated in the hunting horn D.IIIa, were also published by Ferko with this description: "At some undetermined later date, the white bands were painted over with a dark color and superimposed on that new dark band was a large white hunting, or powder horn. This machine was one of those transferred to JG2, Jasta 15. Note there was no spinner on this machine, and it appears to have been flown operationally in that form."
Now, from the collection of Uffz. Hitschler of Jasta 18/57 comes this photo, copied by my late friend Pete Grosz:

That's Hitschler himself, posing with his mechanics and what was certainly his Pfalz at the time. My theory has been that when Hitschler followed
Paul Strähle to Jasta 57 on 28 January 1918, he left his Pfalz D.IIIa behind - and it was then taken over by von Buttlar. Having previously flown a Pfalz D.III with the white man-in-the-moon emblem, Buttlar might have been predisposed to flying a Pfalz D.IIIa. At any rate, von Buttlar soon painted over the white stripes and added his own hunting horn emblem from his coat of arms. The photo of this same striped machine sans Hitschler and crew that Hans posted came from the album of J. Rief, a Jasta 18 mechanic.
The light-colored fuselage underside was pretty universal on these dark blue, red-nosed Albatrosse and Pfalz of Jasta 18 (later 15). It usually extended up to the cowling ring just aft of the propeller spinner; I'm pretty sure it was a light blue on the Albatrosse - the Pfalz might have been pale blue underneath as well, or silbergrau, as Hans says. Personally, I think we're just seeing reflection in the "light-colored" wing root of the von Buttlar D.IIIa. If you'll check the photos above, you'll see what I mean. In all the other Albatros and Pfalz photos I've seen in this scheme, the red and blue fuselage colors came all the way down to the wing root. Usually the Pfalz (and some of the Albatrosse) had the upper surfaces of both wings painted dark blue.