Two different color genes exist in the Dobermann: one for "black" (B) and one for "color dilution" (D). There are nine possible combinations of these alleles, which can result in four different color phenotypes: black, blue, red, and fawn (Isabella). The traditional and most common color occurs when both the color and dilution genes have at least one dominant allele (i.e., BBDD, BBDd, BbDD or BbDd) and is commonly referred to as "black", "black and rust," or "black and tan". The "red", "red rust," or "brown" coloration occurs when the black gene has two recessive alleles but the dilution gene has at least one dominant allele (i.e., bbDD, bbDd). The "blue" Dobermann has the color gene with at least one dominant allele and the dilution gene with both recessive alleles (i.e., BBdd or Bbdd). The "fawn" coloration is the least common, occurring only when both the color and dilution genes have two recessive alleles (i.e., bbdd). Thus, the blue color is a diluted black, and the fawn color is a diluted red.