Right now, I pick Susan Darcy as Red John.

Note: In season 4, the crimson hat, Darcy shoots the driver then the back seat of the limo.  No officer would do this.  Why?  Because you shoot the tires of a car to disable it.  This shows she has reason to kill Agent Wainwright and the driver.  

This is the 7th episode I have watched and plan to start from the beginning later to revise this theory, if needed.

Red John is a woman.
Red John is jealous of others family happiness.
RJ is a master manipulator.  May have psychological training.
RJ possibly is a sociopath, therefore no morals, just rules.
RJ thinks outside the box as she detects evil in others.
RJ is very cautious and thinks ahead.  She also is able to see life through others eyes.
RJ has contacts inside law enforcement or is an officer/agent.
RJ gets jealous when others credit kills to her or try to "copy cat".