Well I would of also expected the 3 lines of axanthic and some of the caramel albino stuff to all be compatible also but its not. Sulfurs seem to throw very orange BlkEL, fires mostly throw ones with some color, but I've never seen a super lemonback have any color. It's enough were I wouldn't start calling it fact and just say we don't know for sure.... because we don't.
It seems they may be related similarly to how the genes on the YB complex are with the Fire types (Fire, Flame, Sulfer, LB) more like the YB and the Vanilla (Vanilla and Disco) types more like the Specter, Gravel etc... if that makes sense.
Specters and gravels while on the same allele as a yellowbelly have their own super form, so the comparison doesn't work
It does because Vanilla and Disco have different super form that is not BkEL and not Vanilla Cream. Also there really do not seem to be enough Supers of Gravel, Specter etc... to really say it is not an animal to animal variation.
Even then the comparison gets the point across that the BkEL complex may act in a similar fashion to the YB complex.