My guess is that the lime will revert back to normal if it is re-grafted to a non verigated rootstock. Maybe it has had the genes for pigmentation all along, but the rootstock is providing the trigger to activate the supressed gene. Genetics is far more complicated than we like to admit. If it is rootstock controlled, you could start grafting limes on the verigated lemon rootstock and selling them. I wonder what other citrus it would work with? Pomello, grapefruit, kumquat?