The agouti series is a set of genes in certain dogs that determines which cells produce black pigmentation. Four different genes exist in the in the series: sable, wildtype, tan points and recessive black. These can result in a range of coat patterns.
Three different coat patterns can arise from the sable gene: clear sable, tipped sable and shaded sable. Clear sables are red dogs with a few black hairs or a black mask; this coat type can be found in great Danes and Lakeland terriers. Tipped sables are red with black hairs, usually on their head, back, ears and tail. Dogs that show this coat pattern include Irish wolfhounds and lurchers. Shaded sables are much the same as tipped sables, but with a larger amount of black, such as shelties and dachshunds.
The wildtype coat pattern sometimes is known as wolf gray or agouti. It's one of the oldest coat patterns in existence. Dogs with this coat pattern have banded hairs, that start out black at the tips then change pigment, usually gray, cream or yellow. As well as on wolves, this coat pattern can be seen on dogs, such as Siberian huskies, keeshonds and Norwegian elkhounds.
The tan points gene can create two different coat patterns: traditional tan points and the saddle pattern or creeping tan. Dogs with traditional tan points are either black, brown or dilutions of these colors, and have tan markings on their cheeks, the underside of their muzzle, above their eyes, on their chests and legs, and underneath their tails. The most well-known examples of this coat pattern come from dobermans and rottweilers. Dogs with the creeping tan or saddle coat pattern are born black and tan. They start out with a lot of black on them, but this recedes gradually so they're left with a black saddle marking on their backs. Dogs that can have this coat pattern include German shepherds and corgis.
The recessive black coat pattern is rare. Dogs with this gene will be all black, but -- unlike other kinds of black dog -- may genetically have a sable, wildtype or tan pointed coat. They will be unable to display their true coat color due to their recessive black gene. Dogs that can have this coat pattern include Shetland sheepdogs, Samoyeds, German shepherds and pulis.