With the exception of the Palomino, the five new color breeds that have debuted in the game are made-up. How else could we get fun colors like Cerulean and Fantasia? We've also got the Smoke Horse, which is a Black Beauty, and the white Coconut Horse, aptly named as half-shelled coconuts are a well-known sound effects trick for mimicking a trotting horse.
All of these horses can be purchased only after building a Horse Stable, which costs 800 Coins. The Fantasia and Cerulean are Facebook Credits exclusives requiring 78 FB Credits, and they're bought for looks alone, as they've the lowest selling price out of the 5 breeds. But as far as daily maintenance goes, horses are now the pet that earns the most daily XP for players.
Completing the Horse Stable will also get you a free horse (random gender), called the Light Bay (see image on right).
See the Happy Pets Horse Stable building guide here.