OK, today the endo confirmed what my DDS said, which is that the bluish-black area on my gum under that gold crown is a stain caused by the chemicals they used to place the crown reacting with the amalgam underneath and the gold alloy of the crown. Apparently it can take years to develop, or never develop at all. Some people, like me and maybe you longoftooth, are sensitive to the chemicals. The sensitivity is simialr to getting a stain on your finger from silver or other metal jewelry. With the jewelry of course you just remove it and eventually the stain goes away. Guess we're stuck with our "dental tattoos."