When I apply an effect such as a Color Curve to my clip in Vegas Pro, the effect appears blue at first but moving to the next frame displays the picture correctly until you adjust the curve again which previews blue but it plays correctly. Dropping an effect causes a blue preview although it's not blue when played, this makes it hard to adjust effects as they seem blue once dropped then I have to move a frame then make changes & it turns blue again then move to next frame to see my changes, very annoying. Any advice welcome. (Running Vegas 11 as 12 crashes constantly, this is a new issue after I did a clean install of my system.)

Colors are inverted (look at the flags). May be it is issue of a codec? What kind of video sources you are using?

Let's see a ScreenGrab of the CC FX Control Pane.

G

Canon DSLR codec. Any FX does it, disabling graphic acceleration solves the problem but now I don't have acceleration. I also have the latest drivers. It's not permanent it only does the blue once you drop a FX on a clip if you move in the timeline it goes back to normal. It's just annoying as I drop a curve then I first have to move to fix the preview then I adjust my curve it's blue again until I move in the timeline again. Same system, same drivers only a clean Windows install & now it does this.

In this case, the result will be directly dependent on the:
1st - Quick Time version
2nd - Video card driver version.
Any system changes, including Windows Updates, can lead to unpredictable results. Therefore, the surest remedy is to transcode video on another appropriate format. I usually use the XDCAM HD 422 or XDCAM EX HQ, other people often use CineForm.

The CUDA implementation in Vegas is known to be flaky. I believe most users turn it off.