The photo from Ebetta (the first one) is not artificial at all, it's a copper butterfly. The butterfly marking causes a ring of white or clear (cellophane) fin around the edge of the 'normal' colour. Unless it's actually present in the line you won't get it, so I doubt you'd get any butterflies.
matchstickman47 is right, the most likely outcome is that one of the genes would turn out to be slightly more dominant than the other, resulting in a brood comprised of basically one of those two colours. It's also possible that you'd get a fairly even mixture of blacks and whites. I don't really know what would happen if the genes turned out to be codominant. Generally codominance results in a mixture of both traits on one fish but I don't know how this would work. The only 'grey' bettas I have ever seen are variations on the steel blue or green genes.