Look at my genetic stripe stuff in this thread, thats a recessive trait and has some similarity, the thing about the anthrax is its CRAZY variable. You can get them light or dark. I Love my light one that has those super dark eyes. This guy wants to be a tiger anthrax so bad!
The hets and mostly visual, but not always clear cut. Sometimes its just a slight diffusion of pattern. When you have JUST Granite back its pretty easy to tell them from normals, But when you have poss granite back tigers / sun fires / platinum etc, its hard to distinguish.