It's a minor mutation type gene. A pied ball python is no more inbred than an albino or any other one. Just like some people has ice white blond hair, and some have red hair. Some are recessive genes, and it just so happened to appear when bred to a like gened snake.
Not all snakes have the recessive gene for albino or pied. If they don't carry it, no matter how many times you breed them, they still won't pop out the morph.
I think most morphs were brought over from Africa(that is, I've never heard of one that wasn't seen in wild stock first, but I could be wrong). The original morph would be bred to see if it is recessive or co-dominant etc.
Wolfy