Blood Bays are a rare sight on the equine world. They are not the same as a standard bay horse. In fact, the term is a misnomer. The only way a bay horse can be a blood bay is if they have a recessive gene. These horses are considered rare because only a small percentage are actually a blood bay. In the United States, they are most common in the Clydesdale horse breed.  While some people mistakenly think that a standard bay horse is the same as blood bay, they are in fact different. Blood bays have a dark red hue similar to a chestnut mahogany, while bay horses are darker and more brownish in color.