Just a quick simple check for anyone having serious image issues which have seemingly come out of nowhere…I’ve had this happen on one of my projects before and before you drive yourself crazy make sure that the viewer and canvas windows are set to have a BLACK BACKGROUND. Changing the background to anything other than black (White, Checkerboard 1 or Checkerboard 2) can have a huge effect on the appearance of your footage in both the Viewer and Canvas windows.
Hope this saves someone some time and hair ripping manic confusion.
Black BG:

Checkerboard BG (same effect from white):
