The Leopard Gene in Horses

This information was initially blogged, without photographs, on March 29, 2011.

All genes for white markings produce a wide range of amounts of white. The leopard (Appaloosa) gene produces not only a wide array of amounts of white, but also of patterns. Unlike other spotting patterns, it is often progressive with age.

Because the patterns produced by the leopard gene vary so much, I will spend more than one week on them. This week, I will focus on breaking the patterns down into components, following Sponenberg, and commenting on their distribution and genetics.

In the United States, the leopard gene and the patterns it produces tend to be associated with specific breeds, notably the Appaloosa and Pony of the Americas breeds. The Colorado Ranger and the mustang often exhibit the leopard complex colors, as well.

Worldwide, however, the leopard complex patterns are very widely distributed throughout Europe and Asia as well as the Americas. Further, most breeds which have any of these patterns have all of them—a further indication that a single gene is necessary. The only exception at the current time is that a second gene locus, Pattern-1, may be needed to produce the full leopard pattern. A number of other modifiers probably exist, but they are not known. None of these modifiers, however, seems able to do anything without the presence of at least one Leopard allele.

Genetically, the Leopard allele is one of two possible alleles (the other is wild-type) at the Transient Receptor Potential Cation Channel, Subfamily M, Member 1 locus, thankfully abbreviated to TRPM1. This locus is on equine chromosome 1. Leopard is incompletely dominant over wild-type. The locus is called Lp, and the alleles are Lp^Lp (Leopard) and Lp⁺ (wild-type.)

Pattern-1 has not been located exactly, but it may be linked to the Extension locus (determines chestnut) on equine chromosome 3. Pattern-1 increases the amount of white in the coat and is necessary for full expression of the leopard pattern (not to be confused with the Leopard gene.) Yes, the terminology is confusing!

The white sclera and mottled skin show clearly on this POA, which also displays varnish marks.

The first set of characteristics produced by the Leopard allele includes mottled skin, striped hooves, and a white sclera in the eye. White ear tips can also occur. These characteristics are not definitive, as other color genes may cause them, but almost all horses with the Leopard gene show at least one of them.

Horses with the Leopard gene may show other white markings, including the normal face and leg markings. If the leg markings are not present, white may still show on the cannon bones in what are generally called lightning marks or lightning stripes.

Another thing the Leopard allele may do is to introduce interspersed white hairs in either of two patterns. Frost gives a fairly uniform distribution of white hairs over the body, most prominent over the hips and in minimal cases only over the hips. Unlike classic roan, the roaning develops after birth and increases with age up to a point. The dark head and legs of classic roan are generally not visible in this pattern. Unlike grey, the horse eventually reaches a relatively stable color.

Snowflake has a similar developmental pattern, but is most prominent on the foreparts and the white hairs are concentrated into small white spots.

Extreme frosty or snowflake patterns may develop into a speckled appearance, white with small colored areas. All leopard-complex roans may also have varnish marks, with areas over bony prominences (notably the nasal bones and hips) retaining dark pigment.

The Leopard allele may also produce larger but symmetrical white markings, generally starting with a few small white areas over the hips and working forward and downward until the whole horse is white, with the flanks and throat being the last areas to lose color. This is the pattern most strongly influenced by the pattern-1 gene. If the pattern-1 allele is present, white is more extensive than if it is not present. Full white is only possible with the pattern-1 allele. These symmetrical white markings are usually present at birth, though they may increase with age.

The Leopard allele can produce colored round or oval spots over the body. In most cases, these are visible only against a roan or white background, but occasionally they can be seen against pigmented areas of the coat. The spots may be darker or lighter than the base coat color.

Surprisingly, these spots are more likely and more numerous if the horse has one Leopard allele and one wild-type allele. If the horse is homozygous for Leopard (has two Leopard alleles) the spots are more likely to be absent or sparse.

Finally, two doubtful or deleterious aspects of the Leopard allele may be noted. First, leopard interacts with black-pigmented hair to make it brittle. The result is the sparse manes and rat tails often seen on leopard-complex horses whose base color is black or bay and who retain dark color in their manes and tails.

Second, homozygotes for the Leopard allele are generally night blind. This is rarely a problem with modern usage of horses, but should be kept in mind if riding a homozygous  Leopard over unfamiliar ground in darkness.

The named horses in Tourist Trap all have the Leopard allele. I’ll describe Raindrop, Token, Splash, Freckles and Dusty as we get to the combinations of leopard markings that each represents. In fact, I’ll give the full color genotypes I’ve given each. The horse on the cover of Horse Power, near the top of the right sidebar, also has the leopard gene., as does Dottie in the story. In fact, Dottie is supposed to be a granddaughter of Raindrop, and inherited both the Leopard and Dun alleles from her.

White Horses

A few horses are all white, with dark eyes and pink skin. These are not to be confused with aged greys, which may have a pure white coat but retain dark or at least mottled skin, or few-spot leopards, which generally have mottled skin. This type of white can occur from the spotting genes we have discussed as producing pintos, especially if more than one type of spotting gene is present. There is also a type of dominant white which is lethal if two copies of the allele are present but which if one white and one wild-type allele are present produces a healthy white horse.

Remember also that many of the dilution genes we have discussed can produce a very pale cream color often mistaken for white, though most of these horses have light eyes.

All white marking genes on horses, from a conservative white star to a white horse with colored ears, seem to work by preventing the pigment-producing cells from getting to parts of the horse’s body. They do not affect or replace other genes for color. Thus no matter how extensive the white markings on a horse, it will still carry alleles at all of the color loci we have discussed. Further, it will pass those alleles on to its foals.

The white spotting genes grouped as “pinto,” “paint” or “parti-color” may occur in any combination consistent with the survival of the foal. (Two copies of the frame allele at the frame locus, for instance, results in white foal syndrome and early death regardless of what else is present.) A horse could easily have one frame allele, together with two each for sabino-1, tobiano and splash. Because the white areas from these alleles tend to affect different parts of the horse, the result could be a white horse. When bred to plain mates, the offspring would probably be spotted.

Horses with spotting due to a single locus can also be white or nearly white if they are close to the extreme version of that pattern. Several of the spotting patterns converge to a “medicine hat” or “war bonnet” pattern with maximal white. This is probably most common in so-called tovero horses—those that combine tobiano spotting alleles with any of the non-tobiano alleles at other spotting loci. In general the ears are the last areas to lose pigment.

There is one type of pink-skinned white with dark eyes that does not appear to produce spotting in the offspring. White to white breedings of this type, however, always produce some colored foals. Examination of the numbers of white and colored foals suggest that two white alleles at this locus are a prenatal lethal—the foal never develops or is aborted so early that the breeder assumes the mare has missed. This type of white is believed to be due to a dominant gene.

Publicity shot of the Lone Ranger with Silver. Note the dark eyes and pink skin.

The white allele seems to have a surprisingly high mutation rate. Thus whites have been produced from colored parents in several breeds, and then reproduced as if they were dominant whites. I do not know whether DNA proof of parentage was available in these cases, however.

I do not believe a gene test has been developed for this type of white. Gene tests at other loci could be very useful, however, in determining what other color alleles the horse carries and could pass on to its foals.

White is a spectacular color and for that reason was popular in the age of horse power for flashy coach or cavalry horses. At least two western heroes — the Lone Ranger and Hopalong Cassidy — rode dominant whites, Silver and Topper. The downside? Keeping a white horse clean may be a problem, and the pink skin may be subject to sunburn.

White hoses are not albinos, although the initial name of the “breed” registry was the American Albino Horse registry. More online information can be found at The American White and Cream Horse and the Camarillo White Horse Association, though there is some question as to whether the two are genetically the same.

Horse Colors: Manchado and Brindle

This time I’m discussing a pair of markings that may or may not be genetic: manchado and brindle. Sorry, I don’t have any photos, but scroll down the White Horse page and look at Figure 8.120 in Sponenberg.

Manchado is in the pinto group if it is genetic, but it has hardly been investigated at all. Sponenberg says it is primarily found in Argentina, but it is found there in several breeds. This is taken by some as indicating an environmental cause, and by others as indicating that Argentineans pay more attention to horse color than do people in other parts of the world.

There is no question that manchado is different from other spotting genes. At first glance, it is a combination of pinto and leopard (Appaloosa) traits, but manchado horses do not have known leopard or pinto genes. The minimal expression is white on the top of the neck, giving a partially white mane, like tobiano. The head and legs normally remain dark. The white areas are crisp-edged, but these white areas normally have round or oval colored spots within them.

There are a few photos on the web, most notably one showing a Throughbred stallion and an Arabian mare, both breeds which are rarely spotted. Sponenberg shows a photo of a Welsh Pony with the Manchado pattern, but does not state whether is particular individual was from Argentina.

Brindle is a little better understood, but not by much. There are three types of bindles, one involving black stripes, one involving white stripes, and one in which the horse is actually a chimera. In the first two cases, much more common genetic mechanisms appear to be necessary.

For black stripes, the horse must have black interspersed hairs, a condition called sooty by geneticists. In most horses, the interspersed hairs are uniformly mixed into the coat or more numerous toward the back of the horse. In a few horses, the black hairs are organized into vertical stripes.

If white hairs are present, as in roans, they may also occasionally be organized into vertical stripes. This is also referred to as brindle, though it is not known whether this type of brindle has any relationship to the type with black stripes. The rabicano  pattern is an example of this type of brindling.

Finally, it is possible that two fertilized eggs are merged in early gestation. The chimera that results actually has tissues with two different DNA sets, and these tend to be arranged in vertical stripes. A brindle of this type could actually combine any two colors found in horses.

A website from White Horse Productions has excellent photos of these and other rare modifiers in horses. Scroll through the entire page.

The Splashed White Gene in Horses

Splashed white is another spotting gene in horses. It resembles tobiano in that the pattern is usually crisp-edged, and there is no tendency for the kind of uneven roaning often seen in sabino. Splashed white is more common in Europe than in North America, but is becoming common in Paints.

The best description of splashed white is that the horse looks as if it had been dipped feet-first in white paint with its head lowered. Minimal white markings may not be recognized as due to a spotting gene. The next stage includes a blaze that widens toward the muzzle and may extend up the sides of the head, white extending above the knees and hocks, and possibly a belly spot. With stronger grades of spotting the entire head is often white, as well as the entire underbody, and eventually only the ears may retain pigment. Eyes are usually blue or have blue chips. Splashed white can be confused with very crisp sabino markings without roaning, but sabino-1, at least, can be identified through genetic testing.

I am sorry I have no photographs of this pattern, but it is rare in North America. Even Sponenberg’s photos are of Icelandic horses. Splashed white can be very difficult to tell from a crisply marked sabino without roaning. The amount of head white would be unusual for a tobiano. In general tobiano markings look as if white paint was dripped over the horse from the top, while the white in splashed white gives more the appearance of coming up from the bottom. The pattern occurs and is being selected for in Paints, and is known in Icelandic horses,  Welsh Ponies, and Finnish Draft Horses. It also is known in the Appaloosa.

Splashed white appears to be associated with deafness in horses, though many splashed whites have normal hearing.

Splashed white is believed to be due to a dominant or incompletely dominant gene, though the wide range of patterns produced by this gene makes genetic studies difficult. There is evidence of at least one white horse being homozygous for splashed white. At the present time, a DNA test for this gene is not available. There is conflicting evidence as to whether this pattern is associated in any way with the KIT locus.

The Frame Gene in Horses

Chestnut paint. This particular horse appears to have the frame allele rather than sabino, judging from the face and lower legs, in spite of the ragged appearance of the spots.

Frame is another type of spotting gene in horses, formerly lumped into overo and sometimes called frame overo. It has nothing to do with the KIT locus, unlike tobiano and sabino-1.

Frame involves patterns of white which do not usually include roaning, though frame may occur in conjunction with other genes that cause roaning. In frame, the white areas tend to be arranged horizontally on the sides of the horse, and almost never cross the back. Frame is also almost the only pinto pattern in which the legs remain pigmented, though normal leg markings may occur.

Like all spotted horses, frame horses may vary from mostly colored to predominantly white. A frame horse will almost always have a wide blaze or bald face, and an apparently unspotted horse with a bald face but no white leg markings is likely to be a minimally marked frame. As the white expands the head may become mostly white and the white areas on the sides may expand to cover most of the horse, with the spine and legs being the last areas to lose color.

Another Frame. Note minimal leg markings with wide blaze and white spots on sides.

Frame is due to a single allele, frame (Fr), at a locus called endothelin receptor b (EDNRB) on equine chromosome 17. The locus has two known alleles, frame (Fr^Fr) and wild-type (Fr⁺). Frame horses, some of which are so minimally marked as to look solid, have one frame and one wild-type allele.

Breeding two frame horses together may produce lethal white foals, with two frame alleles. Such foals are born white, and the part of their nervous systems that controls the lower intestinal tract does not develop properly. They normally die within 72 hours of birth, though most are euthanized as soon as they are recognized. Most breeders avoid mating two frame horses together in order to avoid the production of such foals.

The frame allele can be tested for. Such testing has demonstrated that some genetically frame horses appear to be solid colored. Whether this is due to a suppressor gene or genes or is simply the extreme end of random variation of amount of white is unknown.

(If you’re here because you like horses, my story, Horse Power, is free today on Kindle. Click on the cover in the sidebar.)

The Tobiano Gene in Horses

Tobiano was the first type of white body spotting in horses recognized as being genetically distinct. Like other white markings, it varies widely in extent, with tobiano horses ranging from white with a colored head to normally colored with white hooves and lower legs, and perhaps a white area in the mane or tail. A few tobianos have blue eyes which are apparently produced by the tobiano gene.

The tobiano pattern has relatively crisp-edged white spots that cross the topline. The arrangement tends to be vertical, though not to the extent of a striped pattern. The head normally remains dark, though the white markings seen on non-spotted horses may be present. At times the dark skin extends under the edges of the white patches, giving a “halo” effect. Portions of the mane and tail growing from white areas are normally white, and in fact this may be the only obvious expression of tobiano in a minimally marked horse.

The pattern is due to a dominant allele, tobiano, at the tobiano locus, To. This locus is near but not at the KIT locus on chromosome 3, and a marker test is available. A horse with two copies of the tobiano allele is perfectly viable and not usually whiter than one with one tobiano and one wild-type allele. It is, however, more likely to show “paw prints” or “bear paws”–roan or spotted areas within the white patches.

Tobiano can occur on any base color: intense, dilute, or with interspersed white hairs. It does occasionally have an odd effect in the presence of one copy of the cream gene. The colored part of the coat “breaks up” into patches of dilute and non-dilute hair. This variation of the pattern is called calico. Calico is thought to be due to a dominant gene at a third locus which can only be detected if both tobiano and cream alleles are present. Theoretically, smoky calico should occur with areas of smoky, black, and white, but I cannot find any reference to this color in Sponenberg.

Although tobiano is dominant, tobiano foals are now and then produced by parents that appear non-spotted. On close examination one of these parents is generally a minimally marked tobiano, with extensive leg white and vary little face white.

The tobiano in the video is a good example of the pattern. Note the way the white markings on the neck are carried into the mane, and the way the white patches cross the topline.

White Body Markings on Horses

Any color horse, full color, dilute, or with intermixed white hairs, can have white body markings. These have long been recognized as falling into two categories: leopard (Appaloosa in North America) and pinto (or paint, piebald, skewbald, or parti-colored.) I’ll leave the leopard complex for later, beyond noting that the horses in Tourist Trap have leopard complex markings. For today, I’ll just give a brief overview of the paint/pinto nomenclature.

Tobiano

In British usage, a piebald was a black and white horse, and a skewbald was red and white. This distinction is rarely made today. Rather, the color of the horse—bay, black, palomino, red dun roan silver, or whatever—is followed by the pattern of marking. And there are a lot more patterns recognized today, often due to quite distinct genes, than was the case when I first became interested in horse genetics!

Paint and pinto are in fact synonyms when they are used as descriptive terms, though they have separate breed registries. In North America the word pinto may be more common in the east and the word paint in the west, but either may include any of the patterns of white body spotting.

Probably frame, based on the wide blaze and generally dark legs.

The first breakdown came when tobiano was recognized as being genetically distinct from overo. Then it turned out that there were several genetically distinct patterns being lumped together as overo—just about everything that wasn’t tobiano, in fact. The latest version of Sponenberg gives no less than seven patterns of white body markings, not including the leopard complex or the dark-eyed solid white of the American Albino. I’ll give a very short summary of the seven here, and cover specific patterns and what is known of their genes in later posts.

Tobiano is a relatively clean, crisp spotting with white legs but generally dark heads. White markings tend to be vertical and generally cross the back in all but minimally marked animals.

The frame pattern was once considered typical overo. It is horizontal, tends to affect the head first and the legs last, and white rarely crosses the spine. Frame to frame breeding can produce white foals that die shortly after birth.

Sabino, showing both the ragged outlines and the roaning typical of this pattern.

Sabino-1 horses normally have both face and leg markings, and often have roaned areas as well. They are usually not as crisply marked as tobianos, but they vary widely and confusion with almost any of the other patterns is possible. Roaning often occurs and is an expected part of the pattern.

Splashed white gives the appearance of the horse being splashed with white paint from below. The legs are normally white, and so is the belly area. In addition, white is normally present on the head, often to such an extent that the head is entirely white.

Polygenetic sabino and the form of dominant white that sometimes produces colored areas are not well characterized genetically. but are apparently distinct from the other forms of white spotting.

The final pattern, which is very rare, is called manchado, and has been seen in several breeds in Argentina. In this pattern, white first appears along the top line, and can produce a white mane on an otherwise colored horse. The head and legs tend to stay dark as the white areas grow larger, and there are often dark spots in the white, giving a superficial similarity to some leopard patterns.

All of these patterns vary widely in the amount of white, and all have pink skin under the white portions of the coat. I’ll take them one at a time in later posts.

Other Patterns of White Hairs in Horses

Rabicano under saddle

This week will be a bit of a catch-all, covering a variety of patterns of white hairs that are neither grey, classic roan, face and leg markings, or associated with white spotting. (Varnish roan, for instance, is a leopard gene pattern, and sabino and dominant white may also produce roaning as part of the pattern.) The genetics of none are well understood. Following Sponenberg, I will list and describe them here. Sorry for the lack of photos, but I haven’t even seen all of these patterns myself.

The first, frosty, may be a variant of classic roan, as it is found in the same breeds. In this pattern, the roaning is most pronounced over bony areas such as the hips, and roaning may affect the mane, tail and head as well as the body. “Squaw manes” and “squaw tails” with white hair mixed in often indicate the frosty pattern. Although there is little doubt that the pattern is genetic, it is not well understood.

“Roaned” is used to refer to horses with a scattering of white hairs not due to the roan or grey genes. It is not always possible to distinguish them from minimal classic roans, but they do occur in breeds where roan does not occur.

Rabicano horse, showing the white at the tail base.

White ticking is a much more specific pattern, involving the base of the tail and the flank. It is not progressive and may occur on any base color. Tails with the base white are sometimes referred to as “skunk tails” or “coon tails.” In Spanish the pattern is called rabicano. This pattern is one of the few “roan” patterns to occur in Arabians. Inheritance is thought to be dominant.

Birdcatcher spots are small white spots scattered over a horse’s body. They are named for a Thoroughbred horse, Irish Birdcatcher, who had such spots. They run in families so probably are genetic, but no studies have been carried out.

Rabicano, showing how white hairs are arranged in stripes on the sides.

White striping is very rare in horses. The vertical white stripes may be a form of roan, as seen on the rabicano photos. Or it may simply be an accident of gestation. One striped Thoroughbred in Australia, Catch a Bird, is himself striped but is producing as a classic roan.

Finally, minor white markings may occur as a result of scarring. These are most common with freeze branding or saddle sores, but one pattern, called white lacing, is commonly due to a skin problem called reticulated leuktricia. Most often the growth of white hair in a net-like pattern over the hips and back is preceded by the formation of crusts in the skin, but not always. Both genetic and environmental causes seem to be involved. If you have an Amazon account, you may be able to see Sponenberg’s photos here.

Next week I’ll start discussing the patterns usually called paint or pinto.

This information is an update of an earlier post.

The Roan Gene in Horses

Roan, like grey, is a pattern gene which sprinkles white hair over an otherwise normally pigmented animal. However, the pattern of white hair, the progression with age and the response to scarring are quite different from grey.

It should be pointed out that horsemen use the word “roan” quite loosely. In Thoroughbreds, for instance, it is used as a synonym for grey, particularly rose grey. There are several forms of roan covered by this loose usage, but the one discussed here is classic roan, which is due to the dominant roan gene. Frosty roan, varnish roan, roaned, rabicano and the roaning caused by some white spotting patterns will be discussed separately.

In classic roan the head, legs, mane and tail remain fully pigmented but there is an admixture of white hairs on the body of the horse. Foals are born roan or shed their foal coat to roan, and beyond that point the roan pattern is not progressive with age. In fact, roans may darken with age. They may also change appearance with season, appearing lightest when the coat is shortest and darker in winter coat.

Corn marks (flecks of the base color) are common on roans, and scars often lack roaning. Photographs of wild horses often show this to an extreme, as dominance battles frequently leave extensive scars.

Roan is due to a dominant gene. At one time, the gene was thought to be a lethal when two roan alleles were present at the roan locus, but more recent work has shown this not to be true. The gene itself has not been found, but it is known to be near, if not part of, the KIT locus on equine chromosome 3. There is clear linkage with chestnut at the extension locus, and tobiano is also linked. As an example of this, if a bay roan is bred to a chestnut, most of the foals will be bay roans or chestnuts, with only a few being chestnut roan or bay. Linked genes do not follow the rules of totally independent inheritance. A linkage test for roan is available if you want to know if a roan is homozygous.

Roan is quite variable in its intensity. Now and then a roan foal comes from two parents thought not to be roans, but close examination of the parents generally shows one to be a roan with very little roaning.

Roan may occur on any base color with any combination of diluting genes and marking genes. Black roans are often referred to as blue roans, bay roans as red roans, and chestnut roans as strawberry roans, but there are also references to purple roans, lilac roans, and honey roans. Further, a “red roan” could have either bay or chestnut as the underlying color, while some dark bay roans were called blue roan or purple roan. The modern practice is to put the base color first, followed by “roan.”

Roi (in Homecoming) will someday get a palomino roan mare with leopard (Appaloosa) markings—a horse overlooked by others because of her color but in fact quite a good horse. She is also a good example of the way different color genes can combine.

(The 3 photos on the left were taken at my cousin’s horse farm in Alabama.)

The Grey Gene in Horses

Grey is frequently considered one of the basic colors of horses, but it is more correct to think of it as a pattern of white hairs. Further, it is the only pattern that changes systematically and predictably with age, and one of the few patterns which can hide most other color genes.

The grey locus is well documented, with two alleles. Grey is dominant to wild-type, and is due to a “4.6 kilobase duplication into intron six of the STYX17 (syntaxis 17) locus, on chromosome 25.” The practical meaning of this is that the grey gene can be tested for, and carriers of wild-type identified.

The horse nearer the camera is a grey that has turned pure white, but the dak eyes and muzzle identify it as a grey.

Gray is a pattern of interspersed white hairs that increase in a fairly predictable fashion with age. I say fairly predictable, because there are several patterns of greying, and any genetic controls for which pattern will occur have not yet been found. The speed at which greying occurs is also quite variable, though in most cases a horse is light grey or white by ten years of age. In all cases, however, the greying begins first on the head. This is in sharp contrast to roan, where the horse is born roan and the head remains dark.

Greys can be born almost any color, but when the foal coat is shed, the horse

This photo clearly show the white rear fetlock. With increasing age, this marking will probably remain visible only in the skin color.

can usually be identified as a grey. Other changes are more variable. The foal may be born with red body pigment, and remain red as the white hairs begin to appear, leading to a rose grey—often miscalled a roan. A red foal coat may shed to black, which then greys as the fraction of white hairs steadily increases. Or the foal may be born black, regardless of the genetic color, and then grey from the black.

Some greys develop a white mane and tail early. These horses generally become pure white with age, though their skin normally remains dark.

A famous grey, General Robert E. Lee’s Traveller. Good example of mane and tail remaining dark.

Others retain a dark mane and tail as the body lightens. These individuals may retain some dark shading on the legs and even body for a long time, and some never become entirely white.

Some grays are dappled at the intermediate stages—the body is covered with circular areas of lighter hair surrounded by darker circles. Others are more uniform—iron greys. Many, as they grow older, develop reddish flecks and are called flea-bitten greys. So-called blood marks—larger areas of red coat—may also develop.

Fleabitten grey with blood mark. Note that the fleabitten stage may come after the grey has become pure white.

One down side of grey is that greys are particularly prone to developing melanomas. Usually these are benign, but not in all cases.

It is worth pointing out that all “white” horses with dark skin are actually grey. All other genetic mechanisms for a white coat in horses also produce pink skin.

Greys can have any of the dilution or white marking patterns in addition to the grey pattern. I had a grey and white frame (paint) myself at one point, and while he looked white with slightly darker mane

Grey aged to white

and tail, the frame markings stood out sharply when I bathed him—the skin under the grey areas was black, while that under all of his white markings was pink. He eventually developed a flea-bitten pattern only over the dark skin.

Two greys are mentioned in Homecoming. The first is Derik’s grey, probably a dappled grey. Coryn took the paralyzed Roi for a ride on the second, Cotton, a horse aged to pure white. The novel I’m currently working on, Rescue Operation, will have two greys, an iron grey called Shadow and a dappled grey called Silver. Both are descended from Arabian stock allowed to run wild on a plateau for a couple of hundred years.