But I think a very recent Windows update is responsible for this strange behaviour.
Suspecting as much when I read your post, I went to Personalization and changed from my normal, neutral grey background to Spotlight and it seemed to work OK. I noticed that I could alter the destop picture from the Settings home screen - no need to go into Personalization. This is new.
Fun and games when I tried to change it back. I have a dark bluish grey accent colour for taskbar and windows. Taskbar text should be white. All of a sudden the taskbar and window text was half white, half black (and almost unreadable). I silently cursed you. 
Anyhow, after fifteen minutes of trying various combinations I restored my neutral, easy-on-the-eyes colour scheme and made a restore point.
So I guess, the only thing I can suggest is play around with it. You can chose to combine elements of various Schemes for the look you want. But I can attest that Spotlight is still working, at least on my machine.
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