The Shetland Sheepdog, often known as the Sheltie, is a breed of herding dog that originated in the Shetland Islands of Scotland. Essentially, however, a blue merle dog is a genetically black dog, either black, white, and tan (tricolor). In the show ring, blue merles may have blue eyes; all other colors must have brown eyes. Breeding colours are also a problem for many beginner breeders. In the show ring, blue merles may have blue eyes; all other colors must have brown eyes. Breeding colours are also a problem for many beginner breeders. In the show ring, blue merles may have blue eyes; all other colors must have brown eyes. Breeding colours are also a problem for many beginner breeders. Certain colour combinations can produce unwanted or potentially harmful results, such as mating blue merle to blue merle, which can produce what is called a 'double merle', more likely to suffer from deafness or blindness.