The fawn mutation within the Shafttail Finches is a common mutation. It is believed that the fawn variety is a color mutation qualitatively changing the appearance of eumelanin pigment from black to dark brown as a result of its incomplete oxidation. The inheritance of the fawn mutation is recessively sex-linked. This means that a fawn mutant from two normally colored parents will always be a female. Fawn males are rare because they can only be born from a fawn mother and a normal father that has been split to this mutation, and of course, from parents that are both the fawns.