I found this while browsing the net, this is part of what I've read:
Leucisism, Hypomelanism, Pastel, and Translucism are all real mutations.
Leucistic, Snow, and Pastel are all Hypomelanistic traits, meaning they lack the dark or black pigment. Translucent dragons lack white pigment and have solid black eyes. As babies, you can see right through their belly!
Leucistic: White, No Pattern, Clear Nails.
Hypo: Lacks dark pigment, Clear Nails.
Pastel: Looks Hypo, but with Black Nails
Snow: Looks Leucistic, but with Black Nails
FYI: Hypos are Pastels, but Pastels are NOT Hypo.