There are quite many possible coat colors in German Pinschers : Black and tan, Liver and tan, Red in various shades, Blue and tan, Isabella and tan and Fawn. Owever, few of them are recognized by official organizations. For exemple, many standards only recognize Black/tan and Reds. The AKC allows Blue/tan and fawn in addition of the two "traditional" colors.
The principal locus responsible for German Pinscher coat colors are the D, B and A.
-B locus codes for the expression of Black or Liver. B = Black b = Liver , Liver (b) is the recessive allele.
B/B or B/b = Black base dog
b/b = Liver base dog
-A is the locus that codes wether for Red or for the Tan point patern. at = tan point Ay = red , Red (Ay) is dominant over tan point allele (at) and B locus.
B-/atat = Black and tan (also called : black and rust)
bb/atat = Liver and tan (also called : chocolate and tan, brown and tan)
B-/AyAy = Clear sable (also called : clear red)
B-/Ayat = Ticked sable (also called : stag red)
bb/Ay- = Liver sable (also called : liver red, choco nose, orange, red nose)
-D locus is responsible for the dilution of the based color. D = not diluted d = diluted , D is dominant over d.
B-/atat/dd = Blue and tan (Black/tan dilution)
bb/atat/dd = Isabella and tan (Liver/tan dilution)
B-/Ay-/dd = Blue sable (also called : fawn)
Black and tan (B-/atat/D-) Clear red (B-/AyAy/D-)
Stag red with light ticking (B-/Ayat/D-) Stag red with heavy ticking (B-/Ayat/D-)
Liver and tan (bb/atat/D-) Liver red (bb/Ay-/D-)
Blue and tan (B-/atat/dd) Isabella and tan (bb/atat/dd)
Here is a simplified chart of the possible colors after mating. It only take the A locus into consideration.