Homozygous Creams ("double Dilutes")
When a horse is homozygous, meaning it has two copies of the cream allele, the strongest color dilution occurs.
- Cremellos are homozygous cream chestnuts, and have a cream colored body with a cream or white mane and tail.
- Perlinos are homozygous cream bays, which also have a cream-colored body but a mane and tail that may be somewhat more reddish in color than a cremello.
- Smoky Creams are homozygous cream blacks, and very difficult to visually distinguish from cremellos or perlinos.
All three shades can be difficult to distinguish from one another, and are oftentimes only firmly identified after a DNA test. While both red and black pigments are turned cream, the black pigment retains a little more color and tends to have a reddish or rusty tint. Thus all-red coats are turned all-ivory, all-black coats are turned all-rusty cream, and bay coats have ivory bodies with slightly darker points.
Horses with two copies of the cream allele can be collectively called double-dilutes, homozygous creams, or blue-eyed creams, and they share a number of characteristics. The eyes are pale blue, paler than the unpigmented blue eyes associated with white color or white markings, and the skin is rosy-pink. The true, unpigmented pink skin associated with white markings is clearly visible against the rosy-pink skin of a double-dilute, especially when their coat is wetted down. The palest shades of double-dilute coats are just off-white, while the darkest are distinctly rust-tinged. Their coats may be described as nearly white or ivory in addition to cream.
The off-white coat, pale blue eyes, and rosy pink skin distinguish the coats of double-dilutes from those of true white horses. True white horses have unpigmented skin and hair due to the incomplete migration of melanocytes from the neural crest during development.
No health defects are associated with the cream gene. This is also true of the normal variations in skin, hair and eye color encoded on the human MATP gene. True white coat coloring can be produced by at least half a dozen known genes, and some are associated with health defects. Some genes which encode a white or near-white coat when heterozygous, popularly called "dominant white," may be lethal in homozygote embryos. Another specific mutation on the endothelin receptor type B (EDNRB) gene is associated with the frame overo pattern produces Lethal white syndrome if homozygous, but carriers can be identified with a DNA test.