Chestnut Overo. Looks like frame Overo to me but the only way to know 100% is Test. The info below I copied & pasted from Wikipedia so you could further understand why Im saying the horse is Frame There are at least three genetically different spotting patterns which fall under the "overo" classification: frame overo, sabino overo, and splash or splashed white overo.To complicate matters further, some of the spotting gene patterns can be combined to produce a horse with multiple color traits, such as the tovero
The frame overo
pattern is the most common of the three types of overo patterns recognized in the American Paint Horse
breed A frame overo horse appears to be any solid base color (bay, black, chestnut, etc.) with white irregular patches added, usually with a horizontal orientation. Markings
are often of jagged shape rather than rounded, the white rarely crosses the back, the lower legs tend to be dark, and the tail is one color, usually dark. The head is often white or bald-faced, and blue eyes are not uncommon. The frame overo pattern usually behaves like a dominant
gene, in that when frame overo horses are crossed on nonspotted horses, about half of the foals come out spotted.There are records of frame overos being produced by two nonspotted parents. There is a theory, however, that these "solid" horses simply may be horses with very minimal expression of overo genetics.
Frame overos have sharply defined, irregular, horizontally oriented white patches. As here, they are often bald-faced and white patches seldom cross the topline, creating a "frame" of non-white coat.