Red dun, also called claybank, is a light tan coat with reddish instead of black points and primitive markings. Genetically, the horse has an underlying chestnut coat color, acted upon by the dun gene. Thus, as there is no black on the horse to be affected, the undiluted underlying color is red.

The tell tale sign is the legs from the knees down. If the legs from the knees down were a sort of grey/white light colour – your foal will stay solid coloured – if the legs were black from from the knee down, or very very dark from the knee down – you’ve got a grey.

Grulla quarter horses are rare. Less than one percent of registered American Quarter horses are Grulla’s. Time changes our ideals of what is beautiful.

Conclusion. Grullo horses aren’t a particular breed; they’re just black horses with a dun gene that causes the black to become diluted. They often have primitive markings that give them away, and you can tell them by their gray or mouse coloration.

The only way to guarantee a black foal is to breed two black parents, meaning both parents are a/a. Once you have got the a/a, to get a grulla, the foal then needs to carry a modifier. To be a grulla, the horse must carry the basic body color of a/a, then carry at least one dun gene.

Blue roan horses have a color pattern with a relatively even mixture of black and white hair that creates a blue appearance. Their head and lower legs are typically darker and have little or no white. Blue roan horses are present in many equine breeds.

Generally, grullo foals are born a light tan color with a distinct dorsal stripe.

Once you know what the gray’s base color is, select the appropriate cross on the Color-Cross Chart. Then simply add a 50/50 chance of the foal being gray. For example, if you cross a gray horse with a base color of bay to a chestnut horse, you will get the possibility of a sorrel or black foal.