Agouti fur contains a pattern of pigmentation in which individual hairs have several bands of light and dark pigment with black tips.
In cats, the solid or "self" colored cat is not the most common. More cats have ticked fur than solid colour, and in most of them, the ticked fur alternates with the solid colour in some sort of pattern, which is called tabbying.
First, ticking is the result of the agouti gene (A) which causes the individual hairs to have bands of light and heavy pigmentation. The agouti gene allows full pigmentation when the hair starts to grow, then slows down the synthesis of pigment for a while, and then turns it on for a while. As the hair approaches its normal length and stops growing, pigment synthesis stops. The result is a hair shaft that has dense pigment at the tip, then a band of yellow to orange, then a band of dense pigment, fading to yellow to orange at the root.
The agouti band can be seen in both the eumelanistic (black-based) and phaeomelanistic (red-based) colours. In both cases, the agouti band marks the period where the production of melanin has slowed down. It is fairly well accepted that the colour in the agouti band of a eumelanistically-pigmented hair shaft is still eumelanin, not phaeomelanin, but it is the fact that the granules are sparse and "shredded" that gives them the yellow to orange colour. The agouti band is not an alternation of eumelanin production with phaeomelanin production in the same hair shaft.
In eumelanistically-pigmented hair shafts, the agouti band is normally a drab yellow-beige colour. However, the colour of the agouti band can be a richer orange due to the effect of "rufousing" factors. These are polygenetic factors that have not been isolated and identified, but breeders have been able to select for them to produce "warm" background colours in the tabbies. In particular, the Brown Tabby patterns are genetically Black, but the selection of individuals with strong rufousing has produced a rich brown colour in the ticked hairs.
The mutation that causes solid colour is called non-agouti (a/a), and is recessive. The effect of non-agouti is to suppress the ticking, so the same density of pigment is found all along the hair shaft, except at the root, where it normally begins to fade in any case.
The tabby pattern is determined by the tabby gene (T), which causes the ticked hairs to alternate with stripes, blotches, or spots of hairs of solid colour. The commonly-recognized types of tabby patterns have been given descriptive names:
Mackerel Tabby. Ticked hairs alternate with solid hairs in stripes, as on a tiger. This is the most common tabby pattern.
Classic Tabby. Ticked hairs alternate with solid hairs in a blotched pattern, often with a circular "bullseye" on the side, or a "butterfly" on the back. This is called a Blotched Tabby in the UK.
Ticked Tabby. Ticked hairs are found uniformly over the entire coat, giving a flecked or freckled appearance. This pattern is sometimes called the Agouti Tabby or Abyssinian Tabby.
Spotted Tabby. Ticked hairs alternate with spots or rosettes of solid colour, as on a leopard or jaguar.
The agouti and tabby genes combine with the basic pigments to create the following patterns and colours:
The classic tabby pattern (tb) is recessive to the mackerel tabby pattern (T). The Abyssinian pattern (Ta) is dominant to the mackerel tabby pattern (T).
The agouti and tabbying genes also apply to all the colours generated by the albino series (sepia, mink, and pointed colours), but space does not permit them to be listed here. Associations in the US only recognize Burmese and Tonkinese in non-agouti, eumelanistic colours, so no tabby patterns should be visible in those breeds. The Singapura is recognized only in the Sable Agouti Tabby colour (seal sepia ticked tabby). Tabby patterns have been accepted by some associations in Siamese, and they are called "Lynx Point".