Windows 10 has lost color - Everything is grey

This just happened - suddenly windows has lost all color -- everything is displayed in shades of grey. Weirdly, the login/lock screen is displayed in full color (so we can rule out the monitor).

I've tried restarting to no avail. Also tried reinstalling graphics drivers (AMD R9 390). I've tried searching for the same issue, but I keep on getting that romance/bdsm novel.