The inhibitor gene
Silver comes from a dominant gene called the inhibitor (I). It holds back the pigment in the lower part of each hair, above all the warm, yellowish pigment, so the base of the hair turns white or almost white while the tip keeps its colour. Because the gene is dominant, a silver kitten always has at least one silver parent: silver cannot hide for generations and then suddenly appear. One copy of the gene gives the full effect and two copies look exactly the same, so whether a silver cat carries one or two copies usually only shows in its kittens. A cat with two copies gives silver to every kitten.
Smoke or silver – the pattern decides
The same gene gets different names depending on the pattern underneath. On a solid cat it gives a smoke: from a distance the coat looks solid, but when you part the fur you see a pale undercoat. Black smoke is written ns in EMS. On a tabby cat the pale base and the clear background between the markings give a silver tabby, for example black silver classic tabby, ns 22, or black silver spotted, ns 24. When only the very tip of each hair is coloured, the cat is silver shaded, ns 11, or shell, also called chinchilla, ns 12. In CatCompanion the colour code with s is the same for both, and the app names the cat smoke or silver from the pattern you choose.
Golden is silver's warm cousin
A golden cat has no inhibitor. The look comes from wide-band genes that widen the pale band of each hair, so a tabby or tipped cat gets a warm apricot to golden undercoat with dark tips, for example black golden shaded, ny 11, or black golden classic tabby, ny 22. In several breeds the wide band is inherited recessively, which is why golden can appear in kittens from two non-golden parents. Since golden is the absence of silver, two golden parents can never have a silver kitten. A silver cat mated to a golden one can give both silver and golden kittens, unless the silver parent carries two copies of the inhibitor, in which case every kitten is silver.
Tips for breeders and buyers
Shaded and shell kittens are often born darker, with faint tabby markings that fade as the coat grows, so the final colour is easier to judge at a few months old. In silvers, judges look for a clear, bright undercoat without a brownish or yellowish tinge, often called tarnish, and in goldens for a warm, clear apricot. Plan matings with the pedigrees in front of you: if neither parent is silver, no kitten can be silver, whatever the coat looks like at birth. When you register a cat, write the full EMS code from the pedigree, such as MCO ns 03 22, so breed, colour, white and pattern are all recorded correctly.