I don't have a solution, but pale yellow seems to imply that the Blue component of the RGB signal is not as high as it should be. I'm not a color person, I'm just saying that based on playing with RGB values in GIMP.
Assuming this is an analog electronics problem, then my best guess is that Blue is having some problem changing fast enough - which would explain why it can saturate in time if the background is gray, but not black.
In the closeup photo, it looks like there's a yellow fringe on the leading edge of the white, but only after a stretch where the image was previously black. After it has time to "warm up", it eventually reaches white. So it looks like it's a problem with the Blue line being slow to change it's signal voltage.
I wonder if there's some color test pattern that would add any evidence of a problem on the Blue signal. If you displayed vertical bars in some pattern like
BLACK-RED-BLACK-GREEN-BLACK-BLUE
where each of the colors is a fully saturated (bright) value
then I wonder if there would be a noticeable shading effect on the left edge of the Blue (and whether anything similar would show up with Red and Green)
Anyway that's not an answer on how to fix it, just a theory of what the problem is.
The problem with this idea is that it doesn't explain why it works better in a window.
Windowed mode is probably higher res, so maybe there's a difference in clock frequencies somewhere that factors into this somehow. Or I'm just wrong about what's happening.
I don't know how bad it looks in person, but it's possible this is an artifact of intentional filtering on the card, not necessarily a component failure. Some NVidia cards were known for blurriness caused by filtering they put on the RGB signal lines, probably for FCC compliance reasons.
It could also be a problem with the monitor. Does it happen with other monitors, or with other cards connected to the same monitor? Have you tried a different cable?
