Dog coat

The coat of the domestic dog refers to the hair that covers its body. Dogs demonstrate a wide range of coat colors, patterns, textures, and lengths.
As with other mammals, a dog's fur has many uses, including thermoregulation and protection from cuts or scratches; furthermore, a dog's coat plays an important role in the showing of purebred dogs. Breed standards often include a detailed description of the nature and attributes of that breed's ideal coat.
A dog's coat is composed of two layers: a top coat of stiff guard hairs that help repel water and shield from dirt, and an undercoat of soft down hairs, to serve as insulation. Dogs with both under coat and top coat are said to have a double coat. Dogs with a single coat have a coat composed solely of guard hairs, with little or no downy undercoat.
The terms fur and hair are often used interchangeably when describing a dog's coat, however in general, a double coat, like that of the Newfoundland and most livestock guardian dogs, is referred to as a fur coat, while a single coat, like that of the Poodle, is referred to as a hair coat.

Genetics

Domestic dogs exhibit diverse coat colours and patterns. In many mammals, different colour patterns are the result of the regulation of the Agouti gene, which can cause hair follicles to switch from making black or brown pigments to yellow or nearly white pigments. The most common coat pattern found in modern wolves is agouti, in which the upperside of the body has banded hairs and the underside exhibits lighter shading. The colour yellow is dominant to the colour black and is found in dogs across much of the world and the dingo in Australia.
In 2021, a study of whole genome sequences taken from dogs and wolves focused on the genetic relationships between them based on coat colour. The study found that most dog colour haplotypes were similar to most wolf haplotypes, however dominant yellow in dogs was closely related to white in arctic wolves from North America. This result suggests a common origin for dominant yellow in dogs and white in wolves but without recent gene flow, because this clade was found to be genetically basal to the golden jackal and genetically distinct from all other canids. The most recent common ancestor of the golden jackal and the wolf lineage dates back to 2 million years ago. The study proposes that 35,000 years ago there was genetic introgression into the Late Pleistocene grey wolf from a ghost population of an extinct canid which had diverged from the grey wolf lineage over 2 million years ago. This colour diversity could be found 35,000 years ago in wolves and 9,500 years ago in dogs. A closely related haplotype exists among those wolves of Tibet which possess yellow shading in their coats. The study explains the colour relationships between modern dogs and wolves, white wolves from North America, yellow dogs, and yellowish wolves from Tibet. The study concludes that during the Late Pleistocene, natural selection laid the genetic foundation for modern coat colour diversity in dogs and wolves.
During evolution of the dog from their wolf ancestors, coat colors in dogs were probably the inadvertent outcome of some other selective process, and were not likely initially selected for intentionally by humans. Research has found that tameness brings associated physical changes, including coat colouring and patterning.
Domestic dogs often display the remnants of countershading, a common natural camouflage pattern. The basic principle of countershading is when the animal is lit from above, shadows will be cast on the ventral side of the body. These shadows could provide a predator or prey with visual cues relating to the movement of the animal. By being lighter colored on the ventral side of the body, an animal can counteract this, and thereby fool the predator or prey. An alternative explanation is that the dorsal and ventral sides of an animal experience different selection pressures resulting in differing coloration.

Nomenclature of colours and patterns

Colors

The same colour may be referred to differently in different breeds. Likewise, a same term may mean different colourations in different breeds.

Brown, chocolate, liver

Brown, chocolate and liver are the most common terms used to refer to the bb-dilution of black pigment to a dark brown. Depending on breed and exact shade, terms such as mahogany, midtone brown, grey-brown, blackish brown are used. Sedge and deadgrass are used to describe the desired Chesapeake Bay Retriever color that resembles "that of its working surroundings" as closely as possible.

Red

Red refers to reddish shades of orange, brown, and tan. Terms used include orange, red-gold, cinnamon, tan, and ruby. Genetically a dog called red is usually a clear sable or a ruddy recessive yellow.
In some breeds, "red" refers to what would usually be called brown, chocolate, or liver. A "red merle" is always a liver-based merle. In Australian Cattle Dogs, "red" stands for a densely ticked liver-based colouration with an overall red-grey appearance.

Gold and yellow

Gold refers specifically to a rich reddish-yellow and its variants, whereas yellow can refer to any shade of yellow and tan. Terms used include yellow-gold, lion-colored, fawn, apricot, wheaten, tawny, straw, yellow-red, mustard, sandy, honey, blond, and lemon. Dogs called golden or yellow tend to be recessive yellow, but can also be sable.

Cream

Cream refers to a pale yellowish or tannish colour which can be almost white.

Fawn

Fawn typically refers to a yellow, tan, light brown, or cream dog that has a dark melanistic mask.
With Weimaraners, fawn refers to their typical brownish grey colouration that with other breeds is usually called lilac.

Black

Black is a pure black that can get grizzled as the dog ages, or have a tendency to gain a brownish cast when exposed to the elements.

Blue

Blue is a cool-toned, metallic grey. It typically means a d/d dilution of black pigment, a grey colouration that is grey from birth, but has a wide range of breed-specific meanings.
In Kerry Blue Terriers, Poodles, and Bearded Collies, "blue" refers to colouration that is black at birth and progressively greys out as the dog matures. In Australian Shepherds, Rough Collies, and Shetland Sheepdogs, blue means a blue merle. In Australian Silky Terriers, blue means a saddle-type black and tan pattern, where the black parts of the coat progressively fade to a steel grey as the dog matures and in Australian Cattle Dogs, blue stands for a densely ticked black-based colouration with an overall blue-grey appearance.

Grey

Grey simply means a grey colouration of any shade. It can be used as an alternative synonym of blue, but tends to mean some other type of grey than the d/d dilution of black. Synonyms include silver, pepper, grizzle, slate, blue-black grey, black and silver, steel. Greys of a dusty or brownish cast are often lilac, a d/d dilution of liver, and this colouration does not have much of a commonly recognised name. Across various breeds, it is called lavender, silver-fawn, isabella, fawn, café au lait or silver beige.
In Poodles, a blue is a very slowly fading, very dark steel grey, whereas a silver is a quicker to clear, much lighter grey that can range from a pale platinum to a steel grey. Both are black at birth with minimal markings to indicate future change. Similarly, café au lait is a slower and darker and silver beige a quicker and lighter progressively greying brown, i.e. liver.

White

White: Such a light cream that it is seen and described as pure white, making them distinct from albino dogs. A white dog, as opposed to an albino one, has dark pigment around the eye rims and nose, often coupled with dark-colored eyes. There is often some coat identifiable as cream between the dog's shoulder blades. Extreme piebald dogs can also appear all white, but are caused by a separate factor.

Patterns

The same pattern may be referred to differently in different breeds.

Black and Tan Dachshund	Black and tan Miniature Pinscher	Black and tan, liver and tan, blue and tan: Coat has both colors but in clearly defined and separated areas, usually with the darker color on most of the body and tan underneath and in highlights such as the eyebrows. Black and brindle and liver and brindle, in which the same pattern is evident with brindling in place of tan, are also possible, but less common.
Black and white Border Collie	Blenheim Cavalier King Charles Spaniel	Piebald or pied : any color or pattern coupled with white spotting. This can range anywhere from white toes and tail tip to a mostly white dog with color around the base of the ears and tail. Some breeds have special names for the color combinations; for example, Cavalier King Charles Spaniel uses Blenheim for reddish brown and white. Irish Spotted or flashy pattern is symmetrical and includes a white chest, white band around the neck, white belly, and white feet or "boots". This pattern is commonly seen in herding dogs, and Boxers, among others. The piebald gene is responsible for this pattern.
Extreme piebald Borzoi with small colored patches	Piebald white Dogo Argentino	Extreme piebald or piebald white: an extensive piebald pattern that renders the dog mostly or all white with pink skin. Usually some pigmented specks remain. Governed by the piebald gene.
Tricolor Basset Hound	Tricolor Beagle	Tricolor: Three clearly defined colors, usually either black, liver, or blue on the dog's upper parts, white underneath, with a tan border between and tan highlights; for example, the Smooth Collie, the Rough Collie, the Papillon, or the Sheltie. Tricolor can also refer to a dog whose coat is patched, usually two colors on a white background.
Blue merle tricolor Shetland Sheepdog	Red merle Catahoula Leopard Dogs	Merle: Marbled coat with darker patches and spots of the specified color. Merle is referred to as "Dapple" in Dachshunds.
Tuxedo Lab mix.	Tuxedo Collie mix	Tuxedo: Solid with a white patch on the chest and chin, and white on some or all of the feet The tuxedo pattern is common in dogs that carry only one piebald gene.
Harlequin Great Dane	Harlequin Great Dane	Harlequin: "ripped" splotches of black on white. The Great Dane is the only breed with this pattern. The term harlequin is also sometimes used to describe a piebald spotting pattern, such as parti-colored poodles.
Spotted Dalmatian	Spotted mutt in Sinamaica, Venezuela	Spotted Coin-sized pigmented spots on a white background. The spotting on Dalmatians is unique as it involves mutations in at least three different spotting genes.
Red-speckled Australian Cattle Dog	Liver-ticked German Shorthaired Pointer	Flecked, ticked, speckled: also called belton in English Setters
Orange belton English Setter	Blue speckled Australian Cattle Dog	Flecked, ticked, speckled: also called belton in English Setters
Brown brindle and white Boxer	Very sparsely brindled Great Dane	Brindle: A mixture of black/liver/blue/lilac and red/yellow/cream arranged in a vertical "tiger stripe" pattern.
Airedale Terrier with large black saddle	Norwegian Dunker with merle-affected black saddle	Saddle or blanket: A different color, usually darker, over the centre of the back.
Dark orange sable Pomeranian	Sable Pembroke Welsh Corgi	Sable: Black-tipped hairs overlaid onto a different coloured, lighter background, including grey, silver and gold.
Hairless Chinese Crested Dog	Xoloitzcuintle	Hairless: Some dogs are born without a fur coat.