Pearl or Barlink Factor
Thank you to Ian of Chiron Horses for allowing me to use these photos of his lovely Lusitano horses.
It used to be thought that Pearl and “Barlink factor” were different. Pearl is a dilution of Iberian horse breeds, such as the Andaulusian and Lusitano. Barlink Factor (so called because it is found in horses descended from the Paint stallion Barlink Macho Man, apparently through My Tontime, his granddam) is a dilution found in Quarter Horses and Paints. Recent research has shown that they’re both the result of the same mutation, which most probably originated in Spanish horses and is therefore now referred to as Pearl (although it was briefly called Apricot).
Pearl is recessive with respect to the hair colour, although heterozygotes may have pink patches on the skin. You can see this in the two dark bay horses at the top of the page, which are heterozygous for pearl but just look bay.
Homozygous pearl on a chestnut base coat produces a pale, uniform apricot coloured horse, including its mane and tail. Skin coloration is also pink. This is in contrast to the cream gene, which is semi-dominant, diluting the coat when only one copy is present, but also giving pink skin and blue eyes when homozygous.
Pearl interacts with the cream dilution to produce pseudo double cream dilute phenotypes, including pink skin and blue or green eyes. It is likely that the allele for pearl is a variant at the cream gene, although I haven't yet seen the published evidence for this.
Like with cream, it seems that red pigment is diluted, but black pigment is largely unchanged.
Although I have located several pearl testers I can't find a published account of the pearl gene.