There has been some talk of selectively breeding very dark charcoals... but there's no true melanistic gene yet, which would otherwise be a rather big help in producing an all-black corn. Of course... getting rid of the white checkerboard belly is a problem in and of itself. While it's not too hard to get a fully white ventral side, I've never seen the checker color take over.
Incidentally, anery X blizzard = normals triple het for anery, charcoal, and amel. With amel in the mix, there's no way you'd get an all-black corn, as it removes the melanin.
I recommend, if you're interested in getting into this sort of thing, that you pick up a copy of the 2006 Cornsnake Morph Guide. Excellent info on what makes what, as well as on corn genetics in general.
-Kat
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