Hi, some Yorkie carry a Parti color gene that is recessive. When two dogs that have that recessive Parti gene are bred together they can produce a full Parti color puppy (tri-color white, black & tan) or another Parti carrier puppy. Most puppies who are full Parti colored have much more white than your puppy does so it's possible your puppy is carrying the Parti gene, it does have a large amount of white on it's chest and that white collar on it's neck. You can go to my website to see some examples of Parti colored Yorkies (Gidget, Tuxedo, Dancer, & Checkers) or you can just do a web search for Parti Yorkies - there are lots of examples that should show up. Alot of the Parti Yorkies are from the same bloodlines but not all are. Did either of the parents have alot of white as puppies. The picture in your profile pic looks like the dog has some white on his muzzle.
It's also possible that your Yorkie puppy only has a "mismark" and it's just an odd marking not related to the Parti gene. Please contact me if you have more questions. Good luck with your puppies.
Teresa
Magnum Yorkies, AKC Yorkie puppies for sale