Chinchilla in most small animals is a c-locus mutation, meaning that it is a partial albino. In rats the situation is quite difficult, and chinchilla is a fairly difficult variety to breed due to the interaction of marking and colour genes needed in order to produce the perfect chinchilla.
Colour-wise, black pigment on a chinchilla rat is exactly the same as an agouti, but the unique colour comes from the removal of all of the yellow pigment. This makes the bands that would be red on an agouti a white or pearl-white colour, so the rat becomes a combination of grey and black hairs ticked with white, with black guard hairs.
The genes for removing the yellow pigment in chinchillas only work in combination with a gene for white markings, which is why chinchilla rats are a marked variety. A chinchilla rat has one copy of this spotting gene – a rat with two copies is either never born, or born as a black eyed white type which dies very young.
Genetics: Agouti, with at least one copy of the fading yellow gene, and one copy of the chinchilla spotting gene (A-CscsFy-).
NFRS Standard: Top colour grey, caused by the intermingling of black guard hairs over a pearl white ground. The whole to give a sparkling appearance. Undercolour dark slate blue, intermediate portion pearl, tips black. All the underside to be white with a clear demarcation between top colour and belly. Head markings may be present or absent. Where present either a blaze or a spot to be acceptable. The standard for both is as follows:
Head spot. Head spots to be centrally placed on the rat’s forehead and no bigger than the rat’s eye.
Blaze. This is to be a wedge shaped symmetrical blaze of white starting at the nose and extending up the face to the forehead. The blaze to cover the whisker bed and to taper to a fine point midway between the eyes and the ears. Markings not to extend onto the cheeks or the eyes.
Forelegs to be white to half their length, back feet white to the ankle (hock or tarsal bone). Tails to be pied.
Faults: Drags, yellow or brown tinge to the top colour, skewed or misshapen blazes, uneven or over large head spots.