Here is a link to the wikipedia article about Merle dogs, including a photo of a blind Merle dog--not for the squeamish. It is not only double Merles who have health defects, but a good percentage of single Merles have health defects as well. The percentages are given in this article. Is this the future of the Yorkie breed, creating colors that are pleasing to the eye while the dogs suffer? It is time to contact the AKC and tell them NOT to register off-colored Yorkshire Terriers. The Parti colors, chocolates, sables, and merles are ALL the result of crossbreeding. These color genes have a distinct DNA signature and did NOT arise spontaneously in the Yorkshire Terrier breed--they were bred in from other breeds by unscrupulous breeders.
Merle (dog coat) - Wikipedia, the free encyclopedia