Wow! Neat trick.
The primary colors of a monitor are Red, Green, and Blue.
The other colors are made by adding those colors.
So you managed to ruin two colors at once.
So it is unlikely but not unheard of to be a sudden monitor circuit failure.
Did you unplug the ‘from computer to monitor cable’ when you worked on the computer? If so remove it and check the pins for loose, or pushed-in, or bent pins.
Is the connection tight? Both ends? Some monitors have connections at both ends.
Could you have accidently misadjusted external monitor controls whilst moving things around? Also check the back of the monitor for color adjustment twist knobs.
Did you move the monitor? Degaussing problems would not be screen wide but just in case hit the degauss button. If no degauss button cycle power to the monitor.
Worth a try.
While you’re in there carefully take the video card out and then reseat it. Some people would recommend cleaning the contacts with a pencil eraser. If you do be sure to brush away the excess rubber with a clean non-synthetic cloth.
Do you have another computer where you could swap monitors? Or do so with a friend’s to determine monitor vs computer problem.