In British equestrian use, skewbald and piebald (black-and-white) are together known as coloured, and the white markings are called patches. In North American equestrian usage, the term for all large-spotted colouring is pinto, and the markings are called spots, The specialized term paint refers specifically to a breed of horse with American Quarter Horse or Thoroughbred bloodlines in addition to being spotted, whereas pinto refers to a spotted horse of any breed. Americans usually describe the colouraton of a pinto literally: black-and-white, chestnut-and-white, or bay-and-white.
Genetically, a skewbald horse begins most commonly with a chestnut base coat colour (called "red" by geneticists), or some other set of colour genes other than black. Then the horse has an allele for one of three basic spotting patterns overlaying the base colour. The most common coloured spotting pattern is called tobiano, and is a dominant gene. Tobiano creates spots that are large and rounded, usually with a somewhat vertical orientation, with white that usually crosses the back of the horse, white on the legs, with the head mostly dark. Three less common spotting genes are the frame and splash overogenes, which create a mostly dark, jagged spotting with a horizontal orientation, white on the head, but dark or minimally marked legs. The sabino pattern can be very minimal, usually adding white that runs up the legs onto the belly or flanks, "lacy" or roaning at the edge of the white, plus white on the head that either extends past the eye, over the chin, or both. The genetics of overo and sabino are not yet fully understood, but they can appear in the offspring of two solid-coloured parents, whereas a tobiano must always have at least one tobiano parent.