It's very common for DDR dogs to be dark sable or bi-color, and lots of people have never seen a dark sable GSD. My 19 month old is more than half DDR (sire is pure DDR, dam has some DDR lines) and also a dark sable. Some ask me if he's a GSD mix. Lol.
There are plenty of DDR threads on the board that discuss DDR dogs, maybe you could check them out.
DDR dogs sometimes tend to be more aloof towards strangers, only bonding closely to immediate family members. They do usually have large, heads and muzzles, as well as a large/thickly muscled frame. They are usually medium to low drive, not usually a dog one would choose for sport, such as Schutzhund.
Black/Tan, neutered male
"American Pet Line"
Varick vom Haus Jeffery
Dark Sable, intact male
DDR/West German Show Line