From the Pintabian Registry website:
Horses registered in this division are Pintabian horses. They possess the desired tobiano markings and are over 99% Arabian in blood (but are less than 100% Arabian as purebred Arabians do not come in the tobiano pattern). To qualify for registration in this division, at least one parent must be a tobiano. Four colored photos (one each of the front, rear, right and left sides) must be submitted to the PHRI along with a completed Application for Colored Division Application form and appropriate fee when registering Pintabian horses.
I've seen a lot of horses advertised as Pintabian and seen very few who actually meet this definition of a true Pintabian.