Horse Coat Colours and Genetics: The Complete Guide
By Breedio team
In short
Every horse coat starts from three base colours, chestnut, bay and black, controlled by two genes. Modifiers such as cream, dun, grey, roan and tobiano then change the picture.
Every horse coat starts from one of three base colours: chestnut, bay or black. Two genes, Extension and Agouti, decide which one, and a handful of modifier genes (dilutions and white patterns) then lighten, mix or interrupt that base. Once you know the base and the modifiers, most coat colours stop looking like a long list and start looking like a short set of combinations.
This guide is the pillar of the Breedio coat colour series. Each family of modifiers gets a short section here and a dedicated article for the details.
What are the three base horse coat colours?
Behind every coat sits one of three base colours:
- Chestnut (alezan): red pigment only, from a red body to a liver or flaxen shade.
- Bay (bai): black body pigment restricted to the points (mane, tail, lower legs, ear edges), with a red-brown body.
- Black (noir): black pigment everywhere.
Bay and black are the same black-based horse. The only difference is whether black pigment is restricted to the points or spread over the whole body. Some breeders also use the term brown (bai brun) for a very dark bay. That variation is not covered by the foal coat colour calculator, so treat it as a bay when planning.
Which two genes decide chestnut, bay or black?
Extension (E/e) controls whether black pigment can be produced at all. A horse with two copies of the recessive allele (e/e) cannot make black pigment and is chestnut. A horse with at least one E can make black pigment.
Agouti (A/a) only matters on a black-based horse. The dominant A restricts black to the points, which gives a bay. Two copies of the recessive a (a/a) let black spread over the whole body, which gives a black horse.
| Extension | Agouti | Resulting base coat |
|---|---|---|
| e/e | any | Chestnut (alezan) |
| E/- | A/- | Bay (bai) |
| E/- | a/a | Black (noir) |
Two practical consequences for breeders:
- Agouti is invisible on a chestnut. A chestnut can carry A or a without showing it, and it will pass one of them on.
- An E/E horse can never produce a chestnut foal, because it always passes on E. An E/e horse can.
What do dilution genes change?
Dilutions act on the base coat by lightening pigment. They are the reason a chestnut can be palomino or a bay can be buckskin.
Cream
Cream is incompletely dominant, so the dose matters. One copy turns chestnut into palomino, bay into buckskin (isabelle) and black into smoky black (which often looks black). Two copies give cremello, perlino or smoky cream, with pink skin and blue eyes. Read more in our articles on buckskin genetics, palomino genetics and cremello, perlino and double cream.
Dun
Dun is dominant. It lightens the body and leaves primitive marks: a dorsal stripe, leg barring and shoulder bars. On a bay base it gives bay dun, on chestnut red dun, on black grullo (souris). Per the University of Kentucky Gluck Equine Research Center, dun needs only one copy of the TBX3 dun allele, with no dosage effect. The full story is in our dun and grullo genetics article.
Champagne
Champagne is dominant and lightens both coat and skin: freckled pinkish skin and amber eyes. A heterozygous horse has a 50% chance of passing it on, and a homozygous one always passes it on, as described by the Texas A&M Animal Genetics Laboratory.
Silver
Silver only acts on black pigment. A black-based horse (bay or black) can be diluted, while a chestnut shows no visible effect.
What do the white pattern genes do?
White patterns do not change the pigment itself. They remove or mix pigment in parts of the coat.
Grey
Grey is dominant: foals are born coloured and whiten over the years. A homozygous grey always passes grey, and the grey mutation (an STX17 duplication) means a grey horse must have at least one grey parent. See the grey genetics and greying article.
Roan
Roan is dominant: white hairs are mixed into the body while the head and legs stay dark, and the pattern does not progress with age. Homozygous roans are viable. The Gluck Center notes that at least one parent must be roan. More in the roan genetics article.
Tobiano
Tobiano is dominant. White crosses the topline, the legs are usually white and the head is usually dark. See the pinto article on tobiano, overo and OLWS.
Frame overo and the lethal white risk
Frame overo is caused by a variant of the EDNRB gene. One copy gives the frame pattern, sometimes almost invisible. Two copies cause overo lethal white syndrome (OLWS): the foal is born white with blue eyes and a non-functional gut, develops colic within about 12 hours and dies within days, with no effective treatment (UC Davis Veterinary Genetics Laboratory and veterinary case literature).
Two carriers have a 1 in 4 risk of an affected foal per mating, and a mating between a carrier and a non-carrier cannot produce one. A case report in a solid-coloured Quarter Horse mare showed that a carrier can look solid, so test both parents rather than judging by the amount of white.
Summary: which gene gives which coat?
| Coat | Genes | Inheritance | Series article |
|---|---|---|---|
| Chestnut | Extension e/e | Recessive | This guide |
| Bay | Extension E/-, Agouti A/- | Dominant A | This guide |
| Black | Extension E/-, Agouti a/a | Recessive a | This guide |
| Palomino | Chestnut + one Cream | Incompletely dominant | Palomino |
| Buckskin | Bay + one Cream | Incompletely dominant | Buckskin |
| Cremello / perlino | Two Cream copies | Incompletely dominant | Cremello and perlino |
| Dun / grullo | Dun | Dominant | Dun and grullo |
| Grey | Grey | Dominant | Grey |
| Roan | Roan | Dominant | Roan |
| Tobiano | Tobiano | Dominant | Pinto |
| Frame overo | EDNRB frame | One copy pattern, two copies lethal | Pinto and OLWS |
| Champagne | Champagne | Dominant | This guide |
| Silver | Silver | Acts on black pigment only | This guide |
Why does coat prediction give a range, not one answer?
A coat does not show every gene. A chestnut hides its Agouti status, a grey hides the colour underneath, and a very light coat can hide several genes at once. So from two visible coats, the honest answer is a range of possible foal coats, each with its odds.
Three things narrow that range:
- The parents' own parents. If a bay mare's mother was chestnut, the mare must carry e. A black grandparent shows that a horse can pass a.
- The foals already produced. A past foal often reveals a hidden allele.
- A DNA test. It confirms the genotype for the genes it covers. Labs such as UC Davis, the Gluck Center and Texas A&M offer coat colour panels. Pull 30-50 hairs with the root bulb, from the tail for a foal.
Note that some tests detect a linked marker rather than the causal mutation. The Gluck Center warns this for roan, so concordance is not guaranteed.
How do you check a coat before a mating?
A simple routine for 2026 breeding plans:
- Write down the visible coat of the mare and the stallion.
- Add the coats of their parents if you know them.
- Add any DNA results you already have.
- For any horse with frame overo or from overo lineage, confirm the OLWS status of both parents before the mating.
In France, the coat on the papers is recorded by the SIRE/IFCE, so keep the declared coat consistent with what you enter in your planning.
Try the foal coat colour calculator
The Breedio foal coat colour calculator is free and runs in your browser. Enter the mare's and stallion's coats, optionally their parents' coats and DNA results, and it returns the foal's possible adult coats with their odds. It covers Extension, Agouti, Cream, Champagne, Silver, Dun, Grey, Roan, Tobiano and Frame overo, and warns about the lethal white (OLWS) risk.
Once the mating is planned, the Breedio Gestation Tracker follows each mare through the roughly 340 days of pregnancy, and you can browse all Breedio tools for the rest of the stud workflow.
