Just a suggestion...

If turning off gamma control seems to make the issue better, do two things.

First, go through the setup and accurately set your gamma for your video card and screen. DO NOT just set things up so they look the way you think looks right... I promise you they are not right. Use the setup software that came with the video card, or go to a gamma set screen (Google it) and set the gamma up right on your screen.

Second, go to Scripts -> Partners -> Image Gamma and run that script on everything in your scene. It seems to resolve some odd things that happen with a fiew of the pieces I use.

See if this doesn't give better results. It took me a little while to realize that the super-saturated colors I was accustomed to were not actually all that realistic! Once I got all of this set up right, along with the improvements in the render engine, Gamma works for me. (And if you check my history here in the threads, I was one of the main rabble rousers against GC prior to PP2012!)

Good luck.