Yellow line does not mean GPU is still on.
Yellow line means:
This segment of the sequence does not have a rendered preview file associated with it. Playback will play by rendering each frame just before the CTI reaches it. Playback at full quality will probably be in real time (but it might not be).
So even in software mode you can get a yellow line.
Running Cuda Driver 5.5.28
I can tell by the quality of the picture and the fact that 3:2 pulldown is not being displayed properly that it looks like it does if I leave the cuda card turned on when working in SD.
This is a project that look fine last week, and when opend today I see the issue.
We did update cuda drivers, were gonna rool back and see if it resolves the issue.
The best way to tell if CUDA is on or off is to set up a sample clip with a couple of accelerated effects and export it twice, once with CUDA on and once with it off. If you see a difference in export times, then you know.