My father (caucasion) has had a mostly blueish yet slightly greenish spot on his back for months! He is 6'0" 225lbs and had skin cancer 6 years ago about 8 inches away from this spot, but no OTHER conditions whatsoever in his past. He wants to know how SERIOUS this mark may be but of course as to what exactly it might be. As much advice possible would be appreciated, and bless you for your advice, thanks!