People have already bred YB to fire. It didn't make anything like a superstripe - just looks like an animal that is a YB and a fire at the same time. Superstripes happen because spectre is a different mutation of the same allele as YB's. It isn't technically a homozygous animal, but it has two copies of genes on that particular allele that are both different from each other, as well as different from the wild-type. I believe the same is true of the particular line of "granite" that was bred to a YB to get the ebony. I'm fairly certain we'll see something similar to the mystic potion vs. the super mystic with superstripes when super spectres are produced.