Do you notice that color shift on export, or just in the program monitor?
I've never noticed that myself, with or without MPE enabled. (Mercury PLAYBACK Engine)
Though I certainly do agree that Adobe should move to OpenCL for CS6.
It is in the final render and odd things can happen during the real-time preview as well. CUDA is cool but it needs to mature a bit more. I almost think PP CS 4 was better overall.
There is some good things about the MBE but it is not yet perfect. I think they need to make the transitions CUDA enabled. I think that might help. I agree Open CL might work even better.
I should add that it is not all nested sequences for my system but like others have mentioned in PP CS 4.0 they render fine and preview just fine. CS 5.5 has more realtime but quality should out way performance. I don't know if the MBE should be tweaked out or if Adobe should start from scratch with Open CL as the foundation. Maybe they could call it the Quick Silver Playback Engine. Editing several layers of native AVCHD with filters in high quality is cool but having funky renders really sucks. I am glad I have my CS 4 installed.