The American and the United Kennel Clubs deem all eye colors acceptable for American Pit Bull Terriers but consider blue and mismatched eyes as faults because they indicate that the dog has been crossed with a separate breed. Blue eyes may also signify a disease associated with the merle allele.
The Pit Bull Terrier is the result of breeding Old English Bulldogs with Old English Terriers. In order to make a more competitive dog, some breeders may cross the APBT with the Catahoula Leopard dogs, which result in merle patterns and mismatched colored eyes. While the merle pattern is acceptable when it occurs in other dog breeds, it often exposes the APBT to some health conditions, such as night blindness and hearing problems.
The AKC and UKC have different standards for APBTs, but both kennel clubs agree that a Pit Bull Terrier must be a well-put together dog that is strong and muscular but also graceful and agile. The UKC accepts all color patterns, except for merle, though a coat made up of 80 percent white, tan, liver and black is not encouraged. Other disqualifications and faults under the UKC standard include prick, wide and flat ears, long tails, loaded or upright shoulders or bowed forelegs. A spiney muzzle, splayed feet, curly, wavy or coarse coat, bulging, blue or mismatched eyes and missing teeth are also discouraged.