Dapple Grey Arabian Mare and her dark bay gray foal. Notice lovely seahorse nose shape typical of Arabians! RESEARCH DdO:) - www.pinterest.com... All horse colors are actually built on one of only two base colors, black or chestnut. Various genes act on these colors and dilute them, resulting in a broad spectrum of colors. Gray is common in many breeds: 1 horse in 10 has mutation for graying with age. 3% of Thoroughbreds have gray coats.