Last few days I noticed that after I turn the PC on, when the Lock Screen shows up its black and white (greyscale). I don't know why its this way, or is this a new feature? I did not install a feature update, although smaller updates are set to auto install. This problem does not happen after I sign into the desktop (the desktop is in full color), and if I sign out from the desktop, then the lock screen is also in full color. I searched the internet but couldn't find a solution. This never happened before.
This is my Windows build: Windows 10 Pro, 1903, 18362.356
EDIT: Nevermind. I found out the problem. Windows Spotlight just served me a photo of a picturesque mountain for my lock screen, only that its in black and white. As all other texts (like time, date, weather, default avatar) are also in white, I was fooled into thinking that the display itself has lost its color. Also for some reason, this photo of a mountain stayed around for about a week and didn't change. My bad.