WhisperingWind
For me on "bad screens", what I see around letters is a blue glow.
The first time I was able to notice this was after I used a good screen for a few hours with a pure red screen filter, i.e. blue and green was entirely disabled (NegativeScreen app).
After doing that, I looked at a bad screen again, and both these bluish glows around text and other contrasting items + weird extra "subtle shadows" around UI elements was suuuuuuper obvious to me
Another really interesting difference between bad screens and my "one good screen" is on that good screen, using a pure red screen filter looks entirely red, I do not see any other colors at all even while scrolling.
On essentially all other screens, even though I can confirm that only red subpixels are activated with a macro camera, I still see "green and blue trails" while motion happens on the screen (and sometimes, even when there's no motion, I can see green+blue+yellow colors vibrating at edges of contrasting objects that increases when I move my head around). Macs are especially bad with this. In addition, setting most screens to only use blue pixels will show red motion trails.
I don't think it's the other pixels "secretly" activating, they look like they are disabled, but more about how the way the LCD RGB color filters were physically manufactured somehow creates more than just the color they're supposed to. It also might be connected to LCD response time "overdrive" methods as those are frequently associated with colored motion trails.
The strangest part about this though is how my "one good screen" mysteriously is a total outlier here, since it doesn't have the above issue at all.