The Black was portrayed by a champion Arabian stallion from Texas named Cass-Ole; his friend, the old white horse named Napoleon, was portrayed by Junior - who had previously appeared in National Lampoon's Animal House as Trooper, Neidermeyer's horse.
Cass Ole, like most horses, had his mane trimmed into what's 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 horse's 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.
There is a scene in which Alec opens the door of Henry Dailey's office and looks around at all the old memorabilia Henry acquired as a winning jockey. One of the photos is a shot of a younger Mickey Rooney atop the horse that looks to be the one featured in National Velvet.
The black model horse seen in Alec's bedroom is a Breyer Animal Creations Foundation Stallion #64, produced for 11 years starting in 1977 and retired in 1987.
There is a scene after The Black has jumped overboard and Alec is in the water yelling for help and The Black is swimming towards him. Suddenly the horse begins to tip over, his head plunges underwater and he starts to thrash in the water and his hooves are pawing in the air. This was an accident due to the guide wires being used to control the horse. Too much force was applied on the turn and the horse went under, a serious cause for alarm on the set. To everyone's relief, the horse righted himself and popped up out of the water just fine.
The scene with the cobra took two days to film, because the cobra refused to spread its hood for the longest time. During filming, Kelly Reno was separated from the snake by a pane of glass.