In a previous series of articles, I presented all the basic cat coat colors. I then started a new series of articles about breed-specific colors: for example, the amber color in the Norwegian Forest cat breed. We continue this series with the most recently identified color: the sunshine color. As we will see in the article, sunshine is specific to the Siberian breed and I will explain its properties, its history, and the genetics that make it happen.

Note: Before reading this article, I recommend you to read the articles of the first series on basic cat coat colors: some of the genetic explanations will be useful to understand this article.

The previous articles in the series cover:

What’s the sunshine color?

The sunshine color, previously called golden, is a coat effect that reduces the black pigments in the fur and replaces it with yellow pigments. It gives sunshine cats a very warm and apricot tabby color, hence the name sunshine. When you split the fur, the roots are golden-colored. The color is evolutive, the kittens are born with black markings that will slowly get golden.
The effect doesn’t apply to the paw pads that remain dark, as well as some parts of the fur like the extremity of the tail, and under the paws.
The nose of sunshine cats is pink instead of the characteristic brick color outlined in black for black tabby cats. The muzzle is light cream/white as well as the chest.
The sunshine doesn’t affect solid cats, so a sunshine black solid cat will appear like a normal black solid cat.

Black sunshine blotched tabby from @hilla_siberiancat

As the sunshine is a coat modifier it applies in addition to the base color so a cat can be a black sunshine tabby or a blue sunshine tabby, for example. It can also be present with the colorpoint coat modification as it’s present in the Siberian breed, so a cat can be a black sunshine tabby point.
When a cat is both silver and sunshine they are colloquially called bimetallic and have a specific look. In fact, the cats have a silver tabby look mainly on the back, while the fur looks sunshine on the legs and belly.

Black sunshine silver tabby, also called bimetallic from @leosiberiankittycat

The history of the sunshine color

The first Siberians with a golden look started to appear at the beginning of the 2000s. The first description of the color was made in 2011 by an Italian cat breeder and judge called Eleonora Ruggiero; it was then named “sunshine”. In fact, the term golden could be confused with the golden color present in the Persian and British breeds. It was quickly determined that the golden of the Siberian and golden of Persian breeds were genetically different because of the existence of bimetallic Siberian. In fact, the golden of the Persian breeds cannot coexist with the silver gene.
The sunshine was recognized by the World Cat Federation, an important cat fancy, in 2017.
Finally, the gene responsible for the sunshine color was discovered only in 2021! So you can see that the history of this color is still very recent with a majority of cat fancies that still don’t recognize it. This can lead to confusion in pedigrees as the breeder can’t correctly describe the color of their cats.

Blue sunshine spotted tabby from L’Aurore Sibériale and born at Sib'Aventures

Genetic

The sunshine color is caused by the CORIN gene. This gene is also called the wideband gene because its effect is to widen the golden part of tabby hair leading to a wide golden/apricot band on the hair.
The sunshine allele is recessive and written wb^SIB for Siberian Wideband, while the dominant allele is Wb which corresponds to a non-Sunshine cat. As the allele is recessive the cat needs to be homozygous (aka having two copies of the allele) to be sunshine: wb^SIB/wb^SIB. Non-sunshine cats will be wb^SIB/Wb or Wb/Wb. Cats having one copy of the allele are called sunshine carriers (wb^SIB/Wb), as they have a 50% chance to transmit the sunshine gene to their offspring. Empirically, it seems that sunshine carriers generally have a warm coat color.

Black sunshine tabby from @perseus_purrs

There seems to be some interaction between the effect of the sunshine allele and the silver gene, as silver cats which are homozygous and heterozygous for sunshine both look the same! Only the silver cats homozygous for sunshine should look sunshine in theory, as heterozygous cats are normally non-sunshine. However, because of the interaction of the silver gene, heterozygous cats looks the same as sunshine silver.
The solid gene is epistatic over the sunshine gene: this means that to be sunshine, a cat also needs to be tabby. In fact, a sunshine solid cat will look like a non-sunshine solid cat.
As the sunshine gene is now identified since 2021, some DNA test exists to determine if a cat is sunshine.

Seal sunshine silver tabby point and white from @siberianpelusos

Fun Fact

Golden tigers have a similar mutation of the CORIN gene, it’s in part because of the example of the tigers that the scientist explored the CORIN gene in cats.

Dark sunshine

Some Siberian have a different look than usual sunshine Siberians and have been called “dark sunshine”. In fact, they are darker with more black markings, as well as a dark outline on their nose instead of the usual pink nose of sunshine cats. However, their roots remain golden and different from the ones of a black tabby.
It has been hypothesized that dark sunshine cats are homozygous for the sunshine allele (wb^SIB/wb^SIB) but heterozygous for the agouti gene (A/a), while usual sunshine would be homozygous for the agouti gene (A/A).

Extreme sunshine

Finally, another look has been identified in the Siberian breed and is called “extreme sunshine”. These cats have a more extreme look with white around the muzzle, paws, and belly, and a clearer golden color with fewer tabby markings. They are also born already light in color and similar to adult sunshine.
It was discovered in 2022, that these cats have another allele on the CORIN gene, called Siberian extreme wideband and written wb^eSIB. The extreme sunshine is dominant other the sunshine, so a cat is extreme sunshine if he is wb^eSIB/wb^eSIB or wb^eSIB/wb^SIB.
As the discovery of this new mutation is still very new, a genetic test for the extreme sunshine is not yet available.

Black extreme sunshine spotted tabby from Burian's Secret

Can you have a sunshine cat that is not a Siberian cat?

Researchers have DNA tested different breeds to see if the gene was present in other breeds than the Siberian. The study confirmed that the golden phenotype in the British and Persian breeds is not the same gene.
However, the gene was present in two other breeds: the Kurilian Bobtail and the ToyBob. Both of these breeds have Russian origins like the Siberian. It’s possible that there has been some cross-breeding between these breeds or that the gene exists in the Russian domestic cat population.
As the gene is recessive, it’s very unlikely to find sunshine domestic cats except maybe if the cat is from Russia.

Blue extreme sunshine silver blotched tabby from Burian's Secret

To summarize, sunshine is a recessive gene that widens the yellow pigment on cat hairs. This color is very new and was only genetically identified in 2021 and is present almost exclusively in the Siberian cat breed. There are still some mysteries about the different variations of sunshine, but we can hope to get some answers in future studies.

Two blue sunshine tabby from @vistula.siberians

Sources

On the cover: @perseus_purrs
Caractérisation d’une nouvelle couleur de pelage chez le chat sibérien by Beauvois Hélène, 2020
Beauvois, H., Dufaure de Citres, C., Gache, V., & Abitbol, M. (2021). Siberian cats help in solving part of the mystery surrounding golden cats. Animal genetics, 52(4), 482–491.
Abitbol, M., Dargar, T. and Gache, V. (2022), Golden cats: The story goes on. Anim Genet.
CORIN gene: sunshine and sunshine silver (bimetal) siberians by Messy Beast
The work of Eleonora Ruggiero

The sunshine color: a new color in the Siberian cats