As adults, most gray horses eventually become completely white, though some retain intermixed light and dark hairs.

Some horses develop a dappled pattern for a period of time, others resemble a roan with more uniform intermixing of light and dark hairs.

While gray is classified as a coat color by breed registries, genetically it may be more correct to call it a depigmentation pattern.

[4] Gray also affects spotting patterns of pintos and leopard complex horses such as Appaloosas.

As the horse matures, it "grays out" as white hairs begin to replace the base or birth color.

Usually white hairs are first seen by the muzzle, eyes and flanks, occasionally at birth, and usually by the age of one year.

Some horses develop pigmented reddish-brown speckles on an otherwise white hair coat.

[1] In 2008, researchers at Uppsala University in Sweden identified the genetic mutation that governs the graying process.

The study revealed that all gray horses carry an identical mutation that can be traced back to a common ancestor that lived at least two thousand years ago.

[7] Gray is controlled by a single dominant allele of a gene that regulates specific kinds of stem cells.

[7] The identification of the gray mutation is of great interest in of medical research since this mutation also enhances the risk for melanoma in horses: some studies have suggested as many as 80% of grays over 15 years of age have some form of melanoma.

[10] Growth rate depends on the type, and many are slow-growing, but over time, many develop into a malignant melanoma.

[11] The study of gray genetics has pointed to a molecular pathway that may lead to tumour development.

However, a gray horse with an underlying homozygous cream base coat color may be born with rosy-pink skin, blue eyes and near-white hair.

Varnish roans are created by the action of leopard complex within breeds such as the Appaloosa and are seldom seen elsewhere.

The dilution genes that create dun, cream, pearl, silver dapple and champagne coloring may occasionally result in confusion with gray.

Another cream-colored dilution, the pearl gene or "barlink factor", may also create very light-coated horses.

As part of its legendary dimension, the gray horse in myth has been depicted with seven heads (Uchaishravas) or eight feet (Sleipnir), sometimes in groups or singly.