Felt as though I needed to add my two cents to the discussion:
I asked my wife for the box set as a Christmas gift and she came through for me (and only paid 50 bucks in the process). I was stoked UNTIL I began to read this thread the next day and then I started to worry because there are very few things that I pay attention to more in films than color issues. You can give me a soft picture, too much EE, too dark, etc and I won't care, but I gotta have decent color reproduction. Given everyone's description of the problem, I thought that FOTR was going to look like The Matrix, with its consistent (albeit intentional) green tint.
But I got home from my in-laws, fired up my Mitsubishi HC4000 projector (known for its out-of-the-box accuracy) and took the shrink wrap off the discs. And you know what? I didn't see any of it. No green tint and no overdone blacks. I did as many have suggested and immediately stuck in TTT to compare and it appeared to have an identical palette from what I could see. I even played the scene on the bridge that is repeated from FOTR in TTT back to back and they appeared as close as I can imagine. I'm not saying there's not a green shift happening, but I am saying that it's as much of a non-issue as it can be. Video and audio quality across all the discs is superb. ROTK has never sounded so good - what I used to consider a 'lifeless' soundtrack is now demo quality. If you're waiting for the "Ultimate Edition", all I can say is that it's here, IMHO. The only thing that's missing is an isolated music soundtrack track, but I've long since stopped hoping for that - no one does them anymore for some reason.