Darkening of the gums...RX side effects?

I have recently experienced dark places on my lower gums.   I am on methotrexate, plaquenil, enbrel and ultram.  I have excellent oral hygiene and have never experienced any problems with my teeth.  I went to the dentist yesterday to confirm it was not gum disease or cancer he assured me it was not and went back today a for my cleaning and he had done some research and has not found anything but is thinking it is medicine related since it  has came up since I have started all of the meds and the condition of my teeth and gums is well above the norm.  Has anyone ever experienced anything like this at all?  Help!!! Oh, I am not in any pain around my gums or teeth it just looks really weird.