Windows 10, 1709, fully patched.
Graphics is a nVidia GeForce 750ti.
Today while doing things entirely unrelated to drivers or graphics manipulation (I was running a command prompt, had 20 tabs open in Firefox, and that's about it), my display went from full color to monochrome. It took me a minute to notice, actually, even while I was actively working on the computer.
There were no events in the Event log that seemed to point in any particular direction.
Restarting the computer the logon screen was full color, but about 2 seconds after the desktop loaded, it all went monochrome again.
Locking the computer, the logon screen was once again monochrome, but after the screen turned off for a bit and then I wiggled the mouse and it came back, the logon screen was full color, until I logged in again.
I updated the graphics drivers to the latest (released about a week ago) to no avail.
I'm guessing it's the graphics card, but I'm interested in anyone else has experienced this and might have something else to try first.
I took a screenshot and sent it to my phone, and the screenshot itself was monochrome as well.
Best Answer
Why did my Windows 10 suddenly turn monochrome?
A new shortcut (Windows+Ctrl+C) was added in the Fall Creator's Update that activates colour filters and the default filter is monochrome.
The shortcut is a toggle, so pressing it again removes the filter.
Source Did Windows 10 suddenly turn black & white?