Once in a while you can find Junghans pocket watches with black dials. Mostly the text talks about some military background. As far as my research shows is that these dials are not mentioned at all in the catalogs or price lists which I have seen. What I saw so far is that these black dial watches have a J47b/1 movement installed which puts them after 1938. Lately I got a black dial pocket watch which has a J55 as movement with luminus numbers and pointers.
According to Konrad Knirim there is no proof of Junghans pocket watches with black dials during WWII. The military definded requirements had no black dials for pocket watches. The observation pocket watch, Zeitübertragungsuhr Fl.23884, from Junghans had a white dial. Later during the war there was a need for better readable dials at day, night and under UV light, but these are kind of greenish dials which had zinc sulfide over the hole dial.
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I got hold on one myself. The dial has no other markings beside the "Junghans" logo. The case is fully burnished and has the number 10150 on the outer back lid.