I have a strong feeling that Rossalind Harker is Red John.... there is no proof of her being blind and Red John is clever enough to fool people even Patrick Jane. Infact blindness kind of gives her a cover she seeks. She must have made up the story of Roy Tagliaferro to misguide all. In the episode where the dead guard of the morgue is found in her house... she is seen playing the piano vigorously as if after some victory.... she seems calm and can fool people with her innocense and blindness... besides Red John is supposed to be calculative and good at mind games.......