I am sure you will get some answers from one of our Biewer experts soon. I am not sure in regards to all of the technical aspects of the Biewers, but I think it is safe to say that you are not going to breed to standard colored Yorkies and get a litter of Biewer pups...I would say the two are not even the same breed, but like I said, I don't know that much about them and don't know that the statement would be correct....I think you just have Yorkies w/ a great deal of white on them.
(And really, it's not such a large amount of white that I would have questioned it had you not posted this.)