I can't find the picture now
but I did see an all white yorkie that a lady said she'd created(it had a picture of the mom, very pretty all white long hair). My sister used my computer while visiting and I think she ersased my links! Now I can't find it. She did say it's not recognized by the akc though.
I think a yorkie can be practically black with some white maybe and change over time. I know there were some puppies on here for sale with normal yorkie parents and the puppies had some white on their feet. You just never know.