an interview between Owain Yeoman (Rigsby) and John Troy Donovan (Ron), at this link

http://www.youtube.com/watch?v=0llrwyH08Sg&NR=1&feature=endscreen

 from that link, Owain asks John directly if his character, Ron, is in fact Red John.  Donovan responds by saying, "I can't say...but I think you know, don't you."  To which Owain replies, "Yes, I think we all know."