I have used vetgen in Florida to color test my biewer. Testing for gold is e. Testing for sable is Ay. It is also entirely possible your yorkie isn't either. I owned a very light colored girl who simply did not have the right coat color.
Here's a link to vetgen. They are very fast and usually results are available in a couple of weeks.
VetGen: Veterinary Genetic Services - Canine - List of Services - Coat Color