the graniteback must be from an anthrax parent to be "het anthrax". there are many "graniteback looking" retics out there, but unless they are known to be from a true anthrax clutch, you would have to prove them out.
but assuming you have a pair or true gb het anthrax,
gb x gb = 25% normals, 50% gb's, and 25% anthrax (in genetics theory of course).

the main thing to remember when obtaining a gb or a pair, is to verify that at least one of the parents was anthrax, or that there is a true anthrax somewhere in that "gene pool", so to speak
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retic is king of kings

1.0 Tiger Retic
1.0 Albino Tiger Retic
0.1 Striped Tiger Retic (het albino)
0.1 Salmon Boa
1.0 Albino Boa
0.1 False Water Cobra