Alright I found it.....
Although Appaloosas are most commonly recognized by their colorful coat patterns, they also have other distinctive characteristics. The four identifiable characteristics are: coat pattern, mottled skin, white sclera, and striped hooves. In order to receive regular registration, a horse must have a recognizable coat pattern or mottled skin and one other characteristic. Horses which receive regular registration are issued numbers (no letters precede the number.) Those not displaying a coat pattern or mottled skin and one other characteristic will be classified as non-characteristic (N/C)) and their registration numbers preceded by the letter "N." Horses which complete the Certified Pedigree Option (CPO) program are issued numbers preceded by the letters "CN."
Source:
http://www.appaloosa.com/registration/indentify.htm