Mushroom is a rare and newly discovered dilution that isn’t very well documented. While it looks very similar to (and is usually registered as) silver dapple, it occurs in animals that don’t carry the silver gene.
Mushroom Surprise
Until recently, people assumed the color was silver on a black base, however genetic testing has proved surprising. It turns out that this coloration is actually mushroom working on red pigment or chestnut based animals. The effect of mushroom on black base is unknown.
Mushroom Shades
The newness of this genetic discovery coupled with the fact it has been misidentified as silver for some time makes mushroom quite the mystery. Initially it looks like silver (or chocolate) dapple, however mushroom animals are rarely dappled. When you look closely at an animal with this coloration, they don’t quite look silver. Mushrooms have a very distinct sepia tone and while there is quite a wide variation, their brown is not as rich as silver dapple and not as gold as palomino. It’s similar, but distinct genetically from both silver and cream dilutions.
Admittedly, we think the animals pictured above are mushroom (although the color doesn’t look quite the right shade on either of them). The Shetland at the top is the closest to any of the few mushroom examples we could find.
Mushroom Breeds
Only a few breeds have been identified to carry mushroom, Shetland Ponies are the main breed responsible for the color. Miniature Horses carry it at low frequency. It’s also possible that American Quarter horse, Icelandic horses and Haflingers also carry it, although the Davis genetic testing website doesn’t mention them.