Black and tan is one of the official colors of the Yorkshire terrier recognized by the American Kennel Club, alongside other prominent breed registries.
Having said this, at the time of birth, most of the Yorkies have a black and tan coat that alters in color with age. In the puppies, the coat is primarily black with markings of tan on their undersides and tip of their ears, around their mouth, eyes, chest, and feet.
The color change begins by the time they are six months old, and by the age of 1-2, they would get their permanent coat color. The exact color that the Yorkie would acquire depends on the number of graying genes the dog has, which affects the melanin level. An increased number of graying genes means a paler coloration.
Some would have just one graying gene, and either the blue would dilute to black, or the tan would change to gold, depending upon which color has been affected the most. However, in those with double graying genes, both the black and the tan shades would dilute to a lighter blue and gold coloration, resulting in the blue and gold Yorkie.
Those that retain their black and tan coat in adulthood actually lack the graying gene or don’t have it in significant amounts.
The primary difference is in their coloration. Both have black as one of their colors, while the tan color fades to gold since they have a single graying gene.
