The Ice Age “Yukon Horse” (Equus lambei) is sometimes mentioned when speaking about the silver dilution in horses. In 1993, remains of a 20,000 year-old Yukon Horse were found by miners digging with a backhoe at the Last Chance Creek near Dawson City, Alaska. Although only a portion of the horse was recovered, the hair on the leg and back were preserved, along with a portion of the mane and tail. Because the body color was paler than the legs, but the mane and tail were blonde, some have speculated that the horses may have been bay silvers – or perhaps something like bay silver.
To my knowledge, the remains have never been tested for the silver gene. I did run across this video, though, which has a number of detailed shots of the remains. I found it particularly interesting that there was a dorsal stripe, since that had not been mentioned in any previous information I had encountered. (I should have assumed it was present, given that dun is believed to be the ancestral color of horses, but it was interesting to see it nonetheless.)