Understanding Horse Color: Dilutions
What Is A Dilution?
In color genetics, a 'dilution' is a gene that causes a partial or total lightening of the coat. Chocolate in dogs and ginger in humans are both examples of dilution genes (In fact, some human gingers carry a gene almost identical to the one that makes a dog chocolate).
In horses, there are five known dilution genes - dun, cream, champagne, silver and pearl. Each acts in a different way, although in some cases the results can end up very similar. This is especially the case if a horse has more than one of these genes (and it is possible to carry all five, although pearl and silver, due to the way they act on different base colors, are rarely expressed together).
The dun dilution is, in fact, the original horse coat color. The 'wild type' in horses - the original color - is Extension + Agouti + Dun. Przewalski's Horse is a dun.
The dun gene's status as the 'original color' probably has to do with the fact that dun horses are well camouflaged on the open steppes on which horses evolved.
The dun gene, like agouti, leaves the points of the horse untouched. That is to say, the mane, tail, muzzle, ear tips and lower legs remain dark. On the body, it lightens the pigmentation significantly, but only on one side of the hair. Under a microscope, each hair of a dun horse is distinctly bicolored.
Additionally, the dun gene leaves dark 'stripes' on the horse. The amount of striping varies, but all duns have a dark stripe along the line of the spine from withers to tail head. Loud dun horses, additionally, may have one, more, or all of the following: Cobweb patterning across the face, vertical stripes down the shoulders and barring on the legs just under the knees and hocks. These patterns are referred to as 'dun factor' and there is anecdotal/pedigree evidence that louder patterning exists in horses that have two copies of the gene. Dun is a dominant gene, although it can vary in expression or be masked by white markings.
On a black horse, the dun gene lightens the coat to an even, dark grey. This color is referred to as 'grullo or grulla' in the US and 'mouse dun' in the UK. On darker grullas, the dun markings may be barely visible.
On a bay horse, the dun gene lightens the brown parts of the horse to tan or beige. This color is variously called 'bay dun', 'zebra dun', 'peanut dun' or simply 'dun'. (The word 'dun' is an old English word for brown).
On a chestnut/red horse, the dun gene lightens the body of the coat to a lighter shade of red, whilst the points and dun factor remain darker. This can result in very subtle patterning. I know of one incident where a groom who was unfamiliar with the horse actually tried to 'brush off' it's dun factor, thinking that it had just gotten wet. Dun on chestnut is called 'red dun'.
Cream produces both some of the most gorgeous and desirable colors...and some of the ugliest. This relates to how cream works.
Cream is an incomplete dominant. A horse with only one copy of the gene looks different from one with two.
One copy of cream lightens a brown or red body to gold, with red horses tending to be yellower. It also lightens the mane and tail to cream or white. However, cream does not affect black hair. Therefore, a bay horse with one copy of cream will have a golden body and black points. This color is called 'buckskin' and is sometimes mistaken for dun. However a buckskin horse will either have no dorsal stripe or a very diffuse 'sooty' or 'countershading' stripe.
One copy of cream will lighten the coat of a chestnut horse to gold or dark cream and the mane to light cream or pure white. Called 'palomino', this is one of the most popular horse colors throughout most of the world and is often bred for.
One copy of cream has no effect at all on a black horse - it is completely invisible. When known to carry cream, these horses are sometimes called 'smoky black', but only genetic or progeny testing can identify them.
Two copies of cream have a much greater lightening effect. On a red horse, this produces a cremello or cream, which is an even, light cream all over, sometimes almost white. A bay horse with two copies of cream is light cream, but with subtly darker points - this is called perlino. A black horse with two copies will be a darker, even cream, generally called 'smoky cream'. All double cream horses have pink skin and blue eyes.
Cremello, perlino and smoky cream have traditionally been considered undesirable. They are believed to be 'weak' and are often haunted by the 'blue eyes means vision problems' myth. Some people also find them aesthetically unappealing and they are sometimes mistaken for 'albinos'. Until relatively recently, the AQHA would not register double creams. With greater understanding of genetics, they are now valued, as a cross between, for example, a cremello and a chestnut will always give you a palomino.
The champagne gene was only recently identified and it is still common for champagne horses to be mistaken, visually and phenotypically, for creams.
The effect of champagne is not dissimilar to that of a single copy of cream on bay and chestnut horses. A bay champagne, called 'amber champagne', has a dark gold body (generally darker than buckskin). A chestnut with champagne, generally called 'gold champagne' has a dark gold body with lighter points. Gold champagne, however, seldom lightens the mane and tail all the way to white.
Champagne, unlike cream, does affect the body (although not the points) of black horses, producing 'classic champagne'. This is a smooth dark grey shade similar to grulla, but lacking any dun factor. Despite this, classic champagne horses are sometimes registered as grulla.
The true distinguishing factor of the champagne gene is its effect on the horse's eyes and skin. Normal horse eyes are deep brown from birth. Champagne horses are born with blue eyes that later darken to amber or hazel. Double creams have blue eyes that stay blue. Champagne also causes mottled skin, which is visible on the muzzle, under the tail and around the sheath or udder.
Many champagnes are registered as creams, as not all registries yet acknowledge the color.
Silver or silver dapple is a confusing term, but the one most widely used. The silver gene works quite differently from the other dilutions.
Cream affects black pigment not at all in one dose and less severely in two. Silver is almost the reverse. The silver dilution leaves red pigmentation alone. Silver can, thus, be carried by a red/chestnut without being visible.
On a black horse, silver produces a red-brown horse with a cream or white mane and tail, often undistinguishable from a very dark palomino or a chestnut with a light mane and tail. Bay silvers also have cream or white manes and tails, but their body stays...red-brown. Dapples are often visible on the coat. A horse with two copies of silver is not distinguishable from one with only one.
Yes, it really can be very hard to distinguish a black silver from a bay one. Both are referred to by several regional terms including silver, silver dapple, chocolate and taffy. (Chocolate is the standard term used by the Rocky Mountain Horse Registry - that breed is almost entirely silver).
Unfortunately, the silver gene is associated with equine eye deformities. Two copies of silver often results in cysts within the eye. In most cases, these cysts are benign, but they can sometimes cause vision problems.
The pearl or 'barlink' gene occurs only in Paint horses from the 'Barlink' ranch, Iberian horses and Peruvian Pasos (so far). Pedigree evidence indicates that pearl is a mutation of cream and exists on the same locus (this does not mean horses can only have one or the other, only that they cannot have two copies of both).
Pearl alone has a minimal effect, and is generally invisible on bay or black horses. It can cause some lightening of the coat on chestnut horses. It also produces pink dots on the skin and possibly light brown or amber eyes.
Two copies of pearl produce a horse that looks very much like a champagne if it is bay or chestnut, but on a black ends up looking more like a red dun with no dun factor. Pearl horses are often registered as champagne - or cream dilutions.
One copy of pearl and one copy of cream produces a very light palomino, almost perlino, color on a chestnut horse, and a pale buckskin with tan or brown points on a bay or black. These horses often end up being registered as cremello or perlino, or possibly palomino. Like cremellos and perlinos, they have blue eyes, however, they also have champagne style freckles.
Pearl is confusing, in no small part because it is still being researched. It is also very rare - most likely your horse is not a pearl unless it comes from the bloodlines mentioned.
Cream and pearl has already been discussed, but as mentioned, horses can have multiple dilutions.
Cream plus dun lightens the horse further. The cream gene will also lighten the dun factor, although one of the two most spectacular examples of dun factor I have personally witnessed was on a palomino dun. A red horse with cream and dun may be called palomino dun or dunalino. A bay horse with cream and dun is generally referred to as buckskin dun or dunskin. Such horses may have spectacular bi-colored manes, with the inner part of the mane black and the outer layers cream (although less dramatic frosting of the mane is seen in both duns and buckskins). This coloring is well known in Fjord horses. Black horses with buckskin and dun are normally registered as grulla. Double cream horses with dun are usually registered as cremello, perlino or smoky cream, but I have seen the term 'perlino dun' used in advertising.
Cream plus champagne often results in an extremely light horse with pink skin and blue eyes. Double cream plus champagne horses can even look white and may be mistaken for albinos (true albinism is not recorded in horses and is probably non-viable). Without pedigree testing, these horses are almost always thought to be cremello.
Cream plus silver results in both genes having an effect. This normally produces a horse with a beige or gold body and a light cream or near-white mane and tail, called a 'buckskin silver' or 'silver buckskin'. Black based silver creams tend to be a little darker.
Silver plus pearl usually means only one or the other expresses. As silver does not effect red horses and one copy of pearl only has a very minimal effect on bay or black ones. Silver plus double pearl might produce a horse that resembles a silver cream.
And, yes, it would be theoretically possible for a horse to have cream, pearl, champagne and silver - which would, like silver and double cream - produce a near-white horse with blue eyes.