i always get green clips in my footage when i start color grading and adding fx. i haven't seemed to find a solution until just now. i will bypass all fx and then re enable them and that seems to fix it. this maybe my video card but just thought i would share. video card is a gtx460
This can be an issue with MPEG footage I've seen. Easiest way I've had to get rid of it ( if it's what I think it is ) is to go ahead and put your PreviewRAM to 0, this almost always clears it up for me.