Another recessive mutation at extension was discovered which causes the russet color in Burmese cats.

This phenomenon was first identified in Norwegian Forest cats. Paws and nose still exhibit the original undiluted color, this in contrast to other diluted colors, where paws and nose have the diluted color. Kittens are born dark but lighten up as they age.

A mutation at the extension locus E/e (the melanocortin 1 receptor, MC1R) changes black pigment to amber or light amber, similar in appearance to red and cream.

The existence of this phenomenon as a discrete gene is a controversial subject among feline enthusiasts. The Dilution modifier gene, Dm, 'caramelizes' the dilute colors as a dominant trait.It is different from the browning gene and has only been observed in laboratory cats. Barrington Brown is a recessive browning gene that dilutes black to mahogany, brown to light brown and chocolate to pale coffee.On the left a female kitten, on the right a male adult. Two amber tabby Norwegian Forest cats, showing the colour difference with age. Overview of dilutions in cat coat colors Basic color If the genes are D/D or D/d, the coat will be unaffected. If the cat has d/d genes, the coat is diluted. The d allele is a single-base deletion that truncates the protein. Similar to red cats, all cream cats are tabbies. When a cat has two of the recessive d alleles (Maltese dilution), black fur becomes 'blue' (appearing gray), chocolate fur becomes 'lilac' (appearing light, almost grayish brown-lavender), cinnamon fur becomes 'fawn', and red fur becomes 'cream'. The Dense pigment gene, D/d, codes for melanophilin ( MLPH A0SJ36), a protein involved in the transportation and deposition of pigment into a growing hair. It has been narrowed down to a 3.5 Mb stretch on the X chromosome in 2009. The precise identity of the gene at the Orange locus is unknown. 'Solid' red show cats are usually low contrast ticked tabbies. Orange is epistatic to nonagouti, so all red cats are tabbies. Unidentified 'rufousing polygenes' are theorized to be the reason for this variance. Red show cats have a deep orange color, but it can also present as a yellow or light ginger color. Other common names include yellow, ginger, and marmalade. The pelt color commonly referred to as 'orange' is scientifically known as red. In one study, less than a third of male calicos had a simple XXY Klinefelter's karyotype, slightly more than a third were complicated XXY mosaics, and about a third had no XXY component at all. One in three thousand tortoiseshell cats are male, making the combination possible but rare- however, due to the nature of their genetics, male tortoiseshells often exhibit chromosomal abnormalities. OO results in orange fur, oo results in fur without any orange (black, brown, etc.), and Oo results in a tortoiseshell cat, in which some parts of the fur are orange and others areas non-orange. Since females have two X chromosomes, they have two alleles of this gene. Males can typically only be orange or non-orange due to only having one X chromosome. The orange allele is O, and is codominant with non-orange, o. This gene is located on the X chromosome.

In cats with orange fur, phaeomelanin (red pigment) completely replaces eumelanin (black or brown pigment). The sex-linked red 'Orange' locus, O/o, determines whether a cat will produce eumelanin.

Red silver tabby cat