Hi,
This aircraft was actually marked 'White 1 + ', and an excellent Simon Schatz colour profile of it is featured in an article I wrote, 'Christmas in Courland' (not sure I'm allowed to include a link, but no doubt if you Google it you'll find the article). Also featured there are a couple of photographs. I received some scans of other photographs of this aircraft from Thyben's son, and will publish them in a book at some point in the future.
The Werknummer was 175 045, and it was painted in greys. Simon's profile is the most accurate rendering I'm aware of. Weal is useful as a basic source, but he does make quite a few errors, this being one of them.
Cheers,
Andrew A.