I have gotten several tattoos and they do tend to swell afterward so that by itself would probably not be a big deal. There is a possibility that the discoloration could be bruising, or even leftover ink depending on how thoroughly the area was washed afterward.
However getting a tattoo can be a very dangerous procedure. Since Tattoo Ink is classified as a cosmetic, it is not regulated by the FDA. There is always a risk of allergies and other issues from the ink being put into the skin. Then there is the possibility of skin and blood infections as well. Skin and blood infections can be nasty and spread quickly so if you have any doubts I would recommend getting it looked at by a medical professional.