You might try reading here:
Parti Yorkies - Snow Blue Yorkshire Terriers She has compiled a lot of information and her YT member name is Breezeway. She can help you weed through the difference or the sameness , depending on who you ask.
Just keep in mind that Parti's can be registered with AKC but cannot be shown. YTCA says they should not be bred. Biewers cannot be registered with AKC at this time, but can be registered in other venues.