[MyFairLacy]

I'd be interested in hearing more information about the parents and puppies, along with pictures.

I'm assuming the sire and dam both look like a standard-colored yorkie which is why the OP was surprised by the parti pups. The piebald gene is a recessive gene. The puppy must inherit 2 piebald genes in order to be a parti. If they inherit none or only one, they will look like a standard-colored yorkie but be a carrier of the piebald gene. So for two standard-colored yorkies to produce parti puppies, they must both carry the piebald gene.

You can't breed a "splitter" to a Yorkie and get any biewer puppies. They would all look like standard-colored yorkies. You must breed splitter to splitter or splitter to biewer to get biewer puppies.