What is the difference between a Quarter Horse and a Paint horse?

Very little. The Paint horse began as Quarter Horses that had excessive white markings, in Paint talk these are called 'cropouts'. Two solid colored QHs can and do quite ofter produce a foal that is very colorful. The AQHA has color restrictions, so many of these very nice 'cropouts' were not accepted for registration, making their value much less. So the American Paint Horse Association was born. Since 1965 these wonderful, colorful horses have grown in popularity for their kindness, versatility and beautiful coats.