Michael,
If you are still seeing what was described . . .
For me the Capture Monitor was the only video monitor being affected by nVidia Control Panel settings. Using their html interface under Video & Television select Adjust video color settings. I had to move the Gamma from far left to center AND check “apply these settings to all video technologies”
If your problem is similar, but you are not using nVidia, maybe look for something similar. I was amazed to find that it was impacting the capture monitor . . . and no other.
Steven Bland