Why wouldn't a horse breeder mate male and female palominos to get palomino colts?

Mating two palominos will result in a palomino colt only 50% of the time, with a 25% chance for a chestnut, and a 25% chance for a cremello. Breeding a cremello with a chestnut always gives 100% palomino foals. This will require an explanation of coat colour genetics: When talking about horse coats, there are two dilution genes possible for the foal to inherit. Concerning palominos: The base colour is chestnut. A horse that does not have any dilution genes will be chestnut. A horse that has one dilution gene (the dilute) will be a palomino. A horse with both the dilution genes (double dilute) will be a cremello. When you breed two palominos, two of the possible four dilution genes are in play. This means the foal has a 50% chance of being a palomino (inherits the dilution gene from one parent only), a 25% chance of being a chestnut (inherits neither dilution gene) and a 25% chance of being a cremello (inherits both dilution genes). This means the breeder has only a 50% chance of achieving what they want (foal is palomino). So if a horse breeder is breeding for colour and wants palominos they will choose a chestnut horse and a cremello horse - usually chestnut mares are bred to a cremello stallion, as chestnuts are common. When one parent is a chestnut and one is a cremello, the foal will always be palomino because they will never inherit a dilution gene from the chestnut (it doesn't have one) and they will always inherit a dilution gene from the cremello (because it has both), leaving a single dilution gene for the foal - palomino. Of course, just randomly crossing chestnut mares with cremello stallions does not mean you will always get a stunning golden beauty. The mares and stallions should be carefully matched - if you choose horses that are incompatible in temperament or conformation, you might get a palomino foal that is ugly or belligerent. Colour should not be the first consideration when making breeding choices. Even when you do cross chestnut with cremello (guaranteeing yourself palomino) there is no way to know the quality of the coat colour until the foal is born - you could still end up with a palomino that is too light, too dark, or has a blonde mane and tail rather than true white. So it's best to choose from lines that are known to throw good palominos - or take the 50/50 risk breeding two palominos together.