Change my background back to normal version

Your Phone’s Settings app, look for setting named Wallpaper.

@Gregory0119 You may have turned on Dark Mode in Control Centre, or the Night Shift in Display and Brightness, Settings.

Is this a 24-hour effect, or other?

I just updated with the most recent update and prefer having my mountainous background on my laptop rather than all the bright colors. Can I somehow get the mountains back? I think it was the Mt. Whitney version or something like that.

For some reason my iphone 10 has changed on the calendar from the standard white background to black and the writing is red???