I think Red John is Harker Rosalind. I think she is because if you were red john what would be the best disguise? a blind woman. No one would think a blind woman would be a serial killer. Also because the name is red john everyone's thinking is a man because the john part in the name. Finally her hair is red. So anyone who thinks its her i highly agree with you that she has a very high chance of being red john.
