A 66% or 50% het means that there is a 66% or 50% chance that the animal in question is het for the gene.
If you crossed a 100% het pied to a normal, the offspring would be 50% hets.
If you crossed two snakes that were both 100% het for pied, you would (theoretically) get 1/4 visual piebalds, and the rest would be labeled as 66% hets.