In an isabelle mutation, the amount of eumelanin pigment is reduced. The pigment itself is not changed, but due to a reduction in the pigment concentration, a diluted color is observed when compared with the wild type coloration. The isabelle shafttail's appearance is comprised of soft brown shades. The inheritance of isabelle mutation is autosomal recessive. Autosomal genes come in pairs, and autosomal recessive inheritance means that both genes in a pair are mutant, which causes an isabelle coloration.