I have also had some of the brightly colored specimens from that
"scallop farm" on Cape Cod (actually in a town just this side of Cape
Cod).  It was my understanding that shell color was the actual objective
of the genetic engineering that was done, rather than flavor
enhancement.  Upscale restaurants use them as a "garnish" on the plate
with seafood dinners, not as a main course.  Supposedly the original
market was in Japan, but the idea spread to our west coast, and to other
areas.  It surprised me that Japan was the original market, since
Chlamys nobilis is common there, and that species has naturally
occurring colors that are even brighter than those of the engineered
Pecten irradians.  I don't see why they wouldn't use small, selected C.
nobilis, rather than importing expensive "manmade" scallops from the
other side of the world?  A side effect of the genetic alteration is
that the altered scallop shells are thinner and more fragile than
typical Pecten irradians.
Paul M.