Different dog breeds have very different genetics. Different sizes, features as well as colors. Lots if different genes going on.
The only difference between and normal Ball Python and a morph is the the gene that deals with the pigment in their skin that produces color.
So basically when BP's breed the offspring will get one color allele from the mom and one from the dad. In the case where the dad is a Pastel either his Pastel allele gets passed or his Normal allele does.
If you want to learn more about basic reptile genetics I would recommend checking out this great post: http://ball-pythons.net/forums/showt...Basic-Genetics