100% Het or heterogenous means that the animal is carring one half of the gene it takes to produce the morph. Then there is 50% and 66% that is the percent that they might be het. still with me. So here the odd's. 100% het + 100% het = say four eggs the offspring would turn out like this. 1 pied or 25 % and 2 hets and 1 normal. Now the 2 hets and the 1 normal. Thats where the 66% comes in. two of those snakes will have a 66% het chance. Then there's resesive, Dominate and co-dominate but that gets even worse to understand. for a good idea check out the www.geneticswizard.com
Hope that helps.