But now, a new coat pattern has emerged.
Icelandic horse breeder, Baldur Eiðsson, said he couldn't believe it when the horse, Ellert, was born with a white splattering on his body. The stallion, he says, should have been either bay dun, or blue dun -- like its parents.
'It's not possible to get pinto colors from two one colored parents,' Eiðsson told CNN Sport.
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Ellert, who was born five years ago, takes after his mother's color. But instead of having the typical characteristics of a bay dun Icelandic horse -- with a bay dun body, black mane, tail and primitive markings -- he is 'speckled' white, has a bald white face and partial icy blue eyes.
Freyja Imsland, a genetic expert in Iceland who has worked closely with Eiðsson, explained how Ellert's variant is one-of-a-kind.
'What makes Ellert unique is that he has a variant that is only present in him and his offspring -- this particular change doesn't exist in any other horse in the world,' she said.
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The stallion comes from an outstanding blood line, Eiðsson said, bred from honor-winning blue dun sire Sær frá Bakkakoti and bay dun dam Kengála frá Búlandi. He added that both horses have produced first-class offspring.
'This is unbelievably lucky because these two blood lines are two of the best breeding blood lines in Iceland, coming together to make this beautiful stallion,' Eiðsson added.
Eiðsson said when he was born, they originally thought there had been a mistake during breeding.
'We thought it was a mix up, that the mother had maybe gone to the wrong stallion,' Eiðsson said.
'So we put him to DNA testing and Sær was definitely his father and his mother was Kengála.'
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From there, they carried out genetic testing on Ellert to find out why he was born such a different color to his parents.
Eiðsson said that as a result, they found out Ellert had developed a gene mutation which created this pattern across his body.
'We call it 'ýruskjóttur' which translates to 'speckle',' he added.
Ellert's DNA was sent to Tosso Leeb, professor and director of the Institute of Genetics at the University of Bern.
In 2015, he identified that Ellert was closely related to the 'dominant white' gene -- and characterized the Icelandic horse as the first of its kind with the coat color allele: W21 (or ýruskjóttur.)
Leeb said the white spotting phenotype was 'particularly unique' in Icelandic horses.
'To the best of knowledge this is the first in Icelandic horses and this is special to breeders,' he said, however he cautioned that Ellert's owners would need to be careful during breeding.
'A genetic variant is what I would consider challenging for breeders,' Leeb said, adding that it's not a good idea to try and breed two horses that carry the same gene mutation.
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'As long as horses like this are bred to uniform colored horses that are pigmented all over -- no large markings -- everything will be fine,' he said, adding that if Ellert was bred with another horse with a similar gene mutation -- it would increase the risk of deaf, or unhealthy offspring.
'One has to be careful and one has to be educated about these things,' he said.
New pattern could be wiped out at any moment
Since his birth five years ago, Ellert has already produced four healthy offspring with the same coloring.
However, Imsland said the horses need to be carefully monitored -- as they could be wiped out at any moment.
'If something happened to them it could be the end of the color if it hasn't spread elsewhere,' she said.
'If a volcanic eruption happens, or you have a respiratory infection -- they could all be affected.
'Everything and anything can go wrong so the more the color spreads out, the more safe it would be in terms of genetic diversity.'
A determined Eiðsson wants to ensure Ellert's ýruskjóttur coat is here to stay.
'We're trying to care for all of them in the best way so that they will carry this DNA to the next coming generations,' Eiðsson added.
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Right now, he says, they're focused on finding mares that are just one color for the stallion.
'We are trying to get mares that are single colors so that he can give away his color,' Eiðsson said.
'We want to spread his gene around Iceland -- and the world,' he added.
The farm -- located in Iceland's south -- has already reserved breeding spots with Ellert for next summer.
'People are really excited to breed with him,' Eiðsson said. 'We definitely feel the interest is increasing.'
One of Ellert's trainers, Rósa Birna Þorvaldsdóttir, said that Ellert had been evaluated for breeding with an 8.56 conformation -- which is a score out of 10 rating a horse's bone structure, musculature and its body proportions.
Outside of breeding, she added that Ellert has also begun training again after having covered mares over the summer.
'The goal is to train him well to be shown in a breeding show for riding abilities also,' Þorvaldsdóttir said,
Purebred for over 1,000 years
The Icelandic horse breed was developed after Norse settlers brought horses to colonize their new surroundings in the ninth and 10th centuries.
Known for their distinctive thick and plentiful mane and tail, they boast a finer coat in the summer and a longer, thicker coat in the winter to help protect them from Iceland's biting cold.
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In an attempt to ward of degeneration of stock brought about by crossbreeding, a ban on importing horses into Iceland was introduced around the 10th century -- a law that still stands today.
As a result, the Icelandic horse has continued to be a pure breed for over 1,000 years. And just as no horse can be imported into Iceland from foreign shores, any Icelandic horse to depart the country is also forbidden to ever return.
'Importing a disease could kill off our entire population,' Imsland said.
Domestication led to different horse colors
Imsland said she's spent some time researching ancestral horse colors and the way the animal looked during the ice age. She says domestication has led to more varieties in coat colors.
'In the wild they are prime prey for predators, so they need to have camouflage,' Imsland explained.
'But now that we have domesticated them and they are safe in our keeping,' she says, adding that what was once blue dun, red dun, and bay dun, became bay, black and chestnut.
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'Humans have been guardians and safekeeping of the pigmentation genetic variety in all domestic animals and this is why we have this variety and not all horses look the same.'