Here is the difference between a snake with two copies of a dominant mutant gene and a snake with one copy of a dominant mutant gene. A snake with two copies of a dominant mutant gene mated to a normal snake give different results than a snake with one copy of a dominant mutant gene mated to a normal snake.
Two copies of a dominant mutant gene x two copies of the normal gene produce 100% babies with one copy of the dominant mutant gene paired with one copy of the normal gene (dominant mutant/normal gene pair).
Dominant mutant/normal gene pair x normal/normal gene pair produces
50% dominant mutant/normal gene pair
50% normal/normal gene pair (normal appearance)
Standard genetics uses the term "multiple alleles" when two mutant genes can make a gene pair. For example, the lesser gene and the mojave gene are different mutant genes that can make a gene pair. A geneticist would call a snake with a mojave gene paired with a lesser gene heterozygous because the two genes are not the same.
As far as I can tell from reading various forums, purple / lavender / white albinos in reticulated pythons is another case of multiple alleles. In mice and fruit flies, there are cases of over two dozen mutant genes in a set of alleles.