Yorkshire terriers aren't born with their classic blue and tan coats. As befits such dignified little dogs, they mature into their coats, changing colors throughout their first year. The Yorkshire terrier breed standard for adult dogs calls for a dark steel-blue coat -- most definitely not silver-blue -- and it allows no mixing of lighter hairs within. The dark steel-blue extends from the neck to the tail root, and darker blue hair covers the tail.
Yorkie Puppy Coats
Yorkshire terrier puppies are born with much darker coats than they'll possess at maturity. In some puppies, much of the coat looks practically black. Think of a Doberman pinscher or a Rottweiler's coat -- that's the black-and-tan coloring a young Yorkie has. When he's a puppy, the black and tan hairs of his coat will blend into each other somewhat, but in a Yorkie who's about a year old, the colors are separate and distinct.
Yorkie Coat Changes
A young Yorkie's coat color shift begin at his feet. By the age of 6 months, the feet reveal the breed's classic golden tan. Soon afterward, the same shade appears on the base of his ears. By his first birthday, the black coat should be gone, replaced by one of steel blue, with tan hairs darkest at the roots and lightest at the tips.