Only one type of Yorkie officially exists: the Yorkshire terrier. However, dogs with colors and markings that deviate from the tan coat with the blue saddle also claim to be Yorkies. These dogs are really mismarked Yorkshire terriers or mixes of Yorkshire terriers and other dogs. One breed, the Biewer terrier, is a new breed derived from Yorkshire terriers.
The Yorkshire terrier has been recognized by the Kennel Club in its country of origin since the 1870s and has been recognized by the American Kennel Club since 1885. It is known worldwide as purebred, derived from the now-extinct Paisley terrier and Clydesdale terrier, from whom the Yorkshire terrier inherited the familiar tan coat with steel-blue saddle. The breed may be related to the Skye terrier, which shares the Yorkshire terrier's fine, silky coat. The breed's vibrant personality, small size and attractive coloration make Yorkies popular for mating to other breeds, creating mixes of various types, colors and patterns.
The American Kennel Club accepts four variations of Yorkshire terrier coat color: black and gold, black and tan, blue and gold and blue and tan. No markings are recognized, which means that all Yorkshire terriers are solid-colored dogs with the same saddle pattern (See References 1, 2). The breed standard does permit a "small white spot on the forechest that does not exceed 1 inch at its longest dimension" (See AKC, Breed Standard). While they do not meet the requirements set forth in the breed standard, they are not a different type of Yorkshire terrier breed. These mismarked dogs are not particularly rare and neither are they valuable; however, the make just as wonderful a pet for the right family as a Yorkshire terrier with standard markings.
It has become a common practice to mix different breeds and market them as if the mix was a breed itself. These mixes are often called designer dogs or designer Yorkies. While a Chihuahua mixed with a Yorkshire terrier--called a Chorkie--or a Maltese mixed with a Yorkshire terrier--called a Morkie--might be a cute puppy, it is not a variation of a Yorkshire terrier or a purebred in its own right. It is a mixed breed dog. These dogs are no more valuable than any other mixed breed dogs.
While some breeds will be mixed to make new breeds, such efforts require more than the initial cross to be successful. It can take 20 years or more to develop a breed that resembles the original vision (See Resources 1). Mixed breed dogs do not possess the same physical or mental characteristics as the purebred dogs that are behind them. They may not live as long due to health issues introduced by these random mixes. Due to the traits introduced by other breeds when crossed, they may vary in temperament or trainability from the original breeds, as well.
Some designer Yorkies, called "teacup Yorkies," are actually purebred. These dogs are not special dogs; in fact, they are frequently very ill dogs who may have congenital health issues caused by breeding only for reduced size rather for health or for adherence to the standard. They may have liver shunts, dental issues or brittle bones. Extremely tiny dogs are prone to hypoglycemia, which means that very close attention must be paid to their food intake. These issues and related problems will affect these "teacup" dogs throughout their lives. Breeders who advertise teacups, doll-faced or tiny specialist dogs do so against the ethical code of the breed parent club (See References 2, Teacup Yorkies).
The Biewer (bee-vair) terrier is a striking breed that has its foundation in the Yorkshire terrier. The breed began as a particolor Yorkshire terrier -- a purebred Yorkie with liberal random white markings covering the standard color and pattern. Some questions were raised about the origin of this terrier puppy, Schneeflocken von Friedheck, given that no white dog or dog with white markings had been used in developing the Yorkshire terrier. Once a breeding program for the new breed was established, crosses back to the solid-colored Yorkshire terrier were abandoned.
Because of faulty recordkeeping in the early days of the breed, the Biewer terrier has been established as purebred using the "scientific means," DNA markers that indicate parentage and heritage. It was added to the Foundation Stock Service of the American Kennel Club in April 2014 and will compete in the Toy group when it is officially recognized (See References 3, 4).