Coat
The Kennel Club in the United Kingdom and the American Kennel Club in the United States recognize only two varieties of Chihuahua: the long-coat, and the smooth-coat, also referred to as short-haired. They are genetically the same breed. The term smooth-coat does not mean that the hair is necessarily smooth, as the hair can range from having a velvet touch to a whiskery feeling. Long-haired Chihuahuas are actually smoother to the touch, having soft, fine guard hairs and a downy undercoat, which gives them their fluffy appearance. Unlike many long-haired breeds, long-haired Chihuahuas require no trimming and minimal grooming. Contrary to popular belief, the long-haired breed also typically sheds less than its short-haired counterparts. It may take up to two or more years before a full long-haired coat develops.
Colors
Chihuahuas come in virtually any color combination, from solid to marked or splashed, allowing for colors from solid black to solid white, spotted, sabled, or a variety of other colors and patterns. Colors and patterns can combine and affect each other, resulting in a very high degree of variation. Common colors are fawn, red, cream, chocolate, white, and black. No color or pattern is considered more valuable than another.
The merle coat pattern, which appears mottled, is not traditionally considered part of the breed standard. In May 2007, The Kennel Club decided not to register puppies with this coloration due to the health risks associated with the responsible gene, and in December of that year formally amended the Breed Standard to disqualify merle dogs. The Fédération Cynologique Internationale, which represents the major kennel clubs of 84 countries, also disqualified merle. Other countries' kennel clubs, including Canada, Australia, New Zealand, and Germany, have also disqualified merle. However, in May 2008, the Chihuahua Club of America voted that merles would not be disqualified in the United States, and would be fully registrable and able to compete in American Kennel Club (AKC) events. Opponents of merle recognition suspect the coloration came about by modern cross-breeding with other dogs, and not via natural genetic drift.