Ah, now I found something - the dark brown was added by the British:
Unit: Jasta 15
Serial: 4184/17
This is Pfalz D.III of Ufz. Hegeler of Jasta 15. It was one the last Pfalz D.III ever build.
The plane has a well documented history: Hegeler was shoot down in this plane on February 26, 1918
by Lt. A. Cowper of 24th. Squadron RFC. Hegeler survived the forced landing and was made prisoner.
His intact machine became the subject of several British technical reports. Allocated the British capture
number G141, Hegeler's Pfalz was subsequently re-marked with RFC-roundels. The rear fuselage and
tail unit was doped in PC10 (dark brown olive).
The aeroplane was later displayed at London's Agricultural Hall in Islington between November 1918
and January the following year.
(Source: Wings Palette)