 Cass Ole, like most horses, had his mane trimmed into whats called  a bridle path. This makes it easier to fit a bridle. For the movie,  Cass Ole had to wear "hair extensions" to make his mane look like a  wild horses mane. He also had white markings on his legs and  forehead and the white needed to be covered with a black hair dye to  transform Cass Ole into the Black Stallion.