I'm not sure if you meant to use the word "collar" but Yorkies should wear harnesses to prevent injury to trachea. I personally think the Buddy Belt Harness is the ultimate.
Buddy Belt Harness at Metropawlis Pet Boutique – Unique Products for the Uncommon Pet - Strollers, Carriers, Toys, Collars, Leads, Beds I wished they showed it on a Yorkie, it looks so much cuter. It's made of soft leather, and they sell matching leads. It's easy to put on, it safe and durable.