Well I figured out who Red John is a few weeks ago, but now I just confirmed it (read to the end). I've read all the theories and did not make my own because I didn't want it to have any holes like the others.
Grace has red hair - obvious clue. Now the fact she is away at some computer class thing is suspicious, but not as suspicious as the fact the writers decide to have Rigsby randomly ask Cho on the radio what he thinks she is doing. They joke about it, but why else include that. Obviously this is not enough but I have plenty more. The next thing is I've watched a fair share of TV shows to know how they set stuff up. It would clearly be too boring to have it as one of the department heads of the CBI, or that FBI Brett goon. It would be wild if it was Jane himself, and I gave this a fair shake - the smiley face really does look like him. That would be a little to movie-ish and extreme, but perhaps the writers will use it as a back up. Perhaps they will have to now that I'm uncovering this. But I'm sure they will disclose Red John in an upcoming episode. Anyway there have been many instances where Grace walks in late to work with some phony excuse, and they focus on her with no background noise, very suspicious like. They do this in a lot of shows and it's really subtle. Obviously Grace being Red John is also really unexpected and exciting to please the viewers.
Anyway here's the solid proof you want. Any good TV show or movie that prolongs a character (character delay) for a good long while and makes the character of utmost importance, must attach meaning to the character's name. Usually this comes in the form of scrambled letters. In literature, names have symbolism, just read Death of a Salesman. To make a corny example, the last name of a tough character might be Hardman (Daniel Hardman in suits). Or a fair character may be Alan Balanco (made that one up). But when the character is REALLY important, they tend to scramble the letters, for more of a riddle effect. So we know Patrick Jane comes from a carnival background (too soon?). Now we've seen the closest link, Laurel-eye (she sees Red John, hence the "eye"), getting it? So anyway she is killed in a carnival setting. And the smiley has more blood dripping in the face, because we are getting closer - either Red John trying to hide or some other symbolism - more real, not sure. In any case, if you mix up Grace Van Pelt, you will find not the word Carnival but instead "CARNEVALE", the classic literature form of Carnival. So not only do they put the word carnival, but they use the dramatic form. I cannot see any better solidified proof than this, other shows included. Just imagine Jane saying "CARNEVALE" very dramatically. I'm sure you will one day. It's a nice tough I will say, and it doesn't ruin it one bit for me. My favorite show ever, deservedly so. Good night friends.