Three characters who are in my headcanon half pony, half different type of horses.
Horses exist in the world of Equestria, but not citizens of the kingdom (maybe there's a few scattered about). They mostly live in outside kingdoms, close to the border. Or even main citizens of their own kingdoms.
Hoo'far is the citizen of Saddle Arabia. Saddle Arabians are horses, and similarly to ponies their coats and manes can be colorful, but they don't have cutie marks. They don't have unicorn or pegasus variants, so Hoo'far is an unicorn, as his mother was a Saddle Arabian horse and his father an unicorn.
For both Trouble Shoes and Hammerhead McColt (member of the McColt family), one of their fathers was a wild horse (and for both someone with a work horse body type). Wild horses do not have their own kingdom and live a nomadic lifestyle. Similar to wild ponies (I talked about them: [HERE](https://derpibooru.org/images/2820246?q=artist%3Ainuhoshi-to-darkpen%2C+train)) they don't have cutie marks and they have more natural colors. Trouble Shoes actually looks a lot like his father. Hammerhead is colorwise similar to his McColt relatives. His mother was also a pony with a big body type.
All three of them have cutie marks. Because of their pony heritage they have more magic than their horse counterparts, able to gain one.