Colour Genetics 

I find colours of horses both fascinating and very confusing, especially when you look at the genetic components. 

Last week I was doing a bit of reading and learnt an interesting fact about grey horses. The grey gene is no so much a colour, but rather a gene that causes the base coat to lighten over time. This explains why grey horses are born black, or chestnut, and start to become grey when they lose their first coat. And also why grey horses have more white on them as they get older.

The other fact I read was that horses are all either a red (chestnut) or black base coat, and it is the influence of other genes that cause such variation. So for example, the effect of the dilution gene can cause a chestnut base coat to become palomino. A different set of genes causes the white patterns over a base coat, as in the case of pintos.

I find Otis quite an interesting colour because to the innocent bystander he is a bright bay. But look closer and you will see a scattering of grey hairs throughout his body. His mane is scattered with white hairs, and he has a skunk tail at the top, which suggests to me that he has another gene acting on his coat, such as one of the roan genes.

Following on from this, someone also told me that breeding some colours together increases the likelihood of having a mutated gene, which can result in cremellos, champagnes, and other colours, which could come with associated health problems. They didn`t go into much detail unfortunately, but with the albino yearling in the news recently I`m sure there will be more research in this area.

Much more interesting to me, though, is the difference between a black horse, and a very dark bay horse. Black is surprisingly uncommon, which I already knew, and people often mistake black horses for dark bays. The key to spotting a black horse is to look at the eyes and muzzle. Here the very fine hairs should be jet black. The eyes of a black horse are very dark brown and the skin is black too.  At this time of year, when the horses are shedding their winter coats it`s very hard to spot a black horse because the winter coat is dying, and is thus a dull brown colour. Additionally, some black horses bleach in the sun which means that the horse loses it`s rich black colour, and they resemble a bay. Black horses that do not bleach are called “non-fading”, or “sheer” blacks. The points of a dark horse can also help identify their colour as well, as true black horses have black points, and no red tinges.


At the moment Llani is losing his coat; so is an iron grey, dull brown on his body, whilst his legs are still black. On his face mis muzzle and eyes are black, but the rest of the hair is sun-bleached and falling out. I can`t wait until he has his summer coat!

With all these complications, it`s amazing that breeders can identify the colour a horse will be when they are born. Passports and microchips need to registered within the first six months, so often breeders have to put their best guess. A friend of mine had a foal from her mare who was born a strange blackish brown colour, which became grey in his first winter, and he seems to have matured as a dun. What complications arise if the wrong colour is put on a passport?  And will we soon see a test to determine the genetic coat colour for horses, rather than relying on the visible signs. Or perhaps the coat colour should be left open to confirmation as a yearling? If there is a commonly available test to prove a horse`s colour it could revolutionise horse breeding, as breeders turn towards breeding rarer colours … but then selective breeding could turn into inter-breeding, and that could lead to a whole host of new problems.

Besides, having inside knowledge about colour genes, reduces the element of surprise!

2 thoughts on “Colour Genetics 

  1. Tracy Apr 21, 2015 / 6:42 pm

    Color genetics are fascinating!

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