Am posting this idea two different ways to allow for different possible votes on suspects.

Theory for voting option 1

Have read many times on this site that Heller has been quoted as saying 1) The viewers are going to be disappointed when they learn who the real Red John is 2) Red John is like Waldo hiding in the background and 3) The real Red John appeared in the Mall Scene in Strawberries and Cream Part 2.  With all that in mind, as a viewer from the day The Mentalist aired, I would be most disappointed if Reede Smith turned out to be Red John.  When he was listed as one of the 7 had to refresh my memory as to whom this guy was since he was more in the background than the other suspects.  I have rewatched the Strawberries and Cream mall scene several times and unfortunately the only person I have seen who resembles one of the 7 is someone who looks like he could be Reede Smith :( 
If you have the video, rewatch the conversation between Jane and Bertram when Jane says he believes Red John "has friends all over the state. Powerful friends; I'm serious."  As Bertram shifts around in his chair, a man, very similar in size, shape and looks to Reede Smith, dressed in a reddish shirt, khaki jacket and jeans walks in the background behind Bertram and then behind Jane.  He appears to be carrying a cup of coffee.  Have looked and looked for someone else that resembles the list of 7 but that is all I have been able to find.  

If you think man in background at the mall is Reede Smith thus making him Red John, please click on green for plausible.

Have found a picture of this scene on the web and am posting it under comments.