Impossible to judge colours in isolation based on scanned images -- the same expertized stamp is brown in one pic, grey in the other. Safe to say that in general you need a large number of a stamp before you turn up the rare shades -- and that comparison with other actual stamps, rather than pictures (in catalogue or on screen) is the only good guide to identifying shades. The colours in the stamp pictures in the Michel Germany catalogue are all out of whack in any case.
In the certified stamp above it reads : MiNr. 254d Dunkelgraubraun. Dunkelgraubraun (Töne) is listed as Mi.Nr. 254c Mi.Nr.254d is Schwarz(grau)braun [schwarzgraubraun] So 254d is the the blackbrown.. (error in the certif?)