What is a yellow horse called?

No. As a Equestrianst, and spending much time around horses, there is no "yellow" horse. There is a Palimino coat, which is a pale gold, with white markings, Creamello mane and a creamello tail. Many Palimionos have white facial markings, or leg markings, commonly blazes on the face and socks on the legs around the hooves