Tobiano and Overo are color patterns used to describe Paint and Pinto horses. This description of Tobiano and Overo color patterns was taken from the Pinto Association Web site: www.pinto.org/faqs.html
1) Tobiano (Toe-bee-ah'-no) appears to be white with large spots of color, often overlapping on animals with a greater percentage of color than white. Spots of color typically originate from the head, chest, flank, and buttock, often including the tail. Legs are generally white, giving the appearance of a white horse with large or flowing spots of color. Generally, the white crosses the center of the back or topline of the horse. It is considered necessary to have a Tobiano parent to achieve a Tobiano foal.
2) Overo (O-vair'-o) appears to be a colored horse with jagged white markings usually originating on the animal's side or belly, spreading toward the neck, tail, legs, and back. The color appears to frame the white spots. Thus, an Overo often has a dark tail, mane, legs, and backline. Bald or white faces often accompany the Overo pattern. Some Overos show white legs along with splashy white markings, seemingly comprised of round, lacy white spots. White almost never crosses the back or topline. A horse of Pinto coloration descendant from two solid-colored parents of another typically solid-colored pure breed is called a "crop-out" and is of the Overo pattern.