S.V.
My daughter had this same thing when two of her molars came through. We took her to the dentist. He was great and just said that is was a blood vessel that was above the tooth and so it was pushed to the surface. He said it may be a little painful, but would solve itself in a couple days. We used some orajel and tylenol for a couple of days and the blueish spot went away to reveal the molar that was just fine!