Blue and tan is another AKC-recognized standard coloration of the Yorkshire terrier. They start with the black and tan coat, like all Yorkie puppies. Then, those with a single graying gene would eventually display a light blue coloration, particularly if the black portion of their coat has been affected by the graying gene.
A blue and tan Yorkie would mostly have a blue back and a dark-colored tail, while parts of their face and legs appear tan.