Aalysonh is correct, piebald is just a variation mosaic, it's like saying your glider is a silver mosaic, or a ringtail mosaic, still mosaic. In theory, any mosaic parent can produce one, there has just been a higher prevalence seen in certain lines, the exact inheritance is still being studied and not fully understood. What constitutes a piebald is also slightly debatable, different people will give you different answers. Personally, I would categorize Dartanian as having a "reverse stripe," which is essentially just having white where the black dorsal stripe would be. Some people would probably call that pied, some would not. Regardless, it is a very unique and striking marking, he's a handsome boy for sure.
Here is the link to Pricilla's page on the color:
The Pet Glider
As a side note, some of the more distinct piebalds have sold for somewhere in the range of $3500.
