Im sorry but i don't understand your logic. If it can happen in a aquarium with out any human intervention except that they have no fish to prey on them. Why couldn't it happen in the wild. Its just a gene. The blue jd isnt a dominant gene. Its the same with albinos, i know they are breed easier and more clearer in the aquarium. But they do happen in the wild.
If the gene is there it gets there in some way. If u breed 2 blues u get a normal. Maybe u need 2 realize that there are 3 colorations to the JDs.
Unless the blue has been produced in the lab with hormones or some other things, then i understand ur logic but other wise i think your just being silly.
If u breed a green with a normal u get normals. The normal coloration is a dominant gene. Same if u breed 2 blues, there of spring is normal.
All these things are in there genes, in my opinion our fish in the aquarium don't have any threat to the native population. So i don't see why this breeding can cause and problems. I sure dont know how to gm fish. And i thing gm fish is wrong.