Figure 1. The difference between coat colour gradients, colour polymorphism, and rare colour variants. As an illustrative example, genotypes consist of the B locus = Brown (these variants have reduced eumelanin and appear brownish in colour); D locus = Dilution (causes uneven distribution of the pigment in the fur shaft); A locus = Bengal (the agouti signalling protein switches between black and red pigments, creating a banding pattern in individual hairs); C locus = Colour restriction (through reduced or increased production of melanin). Rare colour variants (in this example the C locus) can become fixed in populations (such as the D locus), after which it may be considered a new Wildtype colour polymorphism.