The Biewer has a set standard created by Mr Biewer from Germany. It's on my website...
www.babyfacebiewers.com if you want to check it out. The color placement on the parti yorkie isn't as specific. Also, Biewers originated in Germany where selective breeding was started. Parti yorkies have an American heritage, I believe. I'm no expert on Parti Yorkies as I own Biewers. You can read about the history of the Biewer there as well. With the Biewer... the color placement is very specific. Hope that answers your question.