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 in their DNA.
Mushroom Dilution
Only a few breeds have been identified to carry mushroom, Shetland Ponies, Haflingers and possibly American Quarter horse and Icelandic horses. Until recently, people assumed the color is silver on a black base, however genetic testing has proved surprising. It turns out that this coloration can actually be mushroom working on 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. Body color is various shades of sepia and mane and tail dilute even lighter.