LauraB is completely correct! And she did a great job with the color explination!
As for the well known "Ratchett", he was what we call a "Frame Overo" with Sorrel coloring.
As for the types of registered paints with the APHA, you have "Regular Registered" Paints, which have atleast the minimal white coloring no less then 2" on the body, then you have the Registered Paints who lack the white color required to be registered as regular paints, registered as "Solid Breed" Paints. Solid breed paints, a while back were referred to as "Breed Stock" Paints. Theres a little more for you!
Dixon's Red Hot Ember