Oh, by the way, there are labs that do testing for coat color genes in Yorkies, including the Biewer trait, but since those are not diseases, they are not included in the database I linked to above.
Oh, and there are also labs that do breed purity testing AND parentage testing. In other words, our dear little Minnie and her parents could be tested to she if she was the offspring of the two reported parents--however, the cost is triple that of a single dog DNA test, so it gets kind of expensive. I only recommend the breed purity test for Minnie for now...
Here's a lab that does coat color and DNA parentage testing for Yorkies:
http://www.healthgene.com/canine-dna-testing/