Taskbar and programs have turned black and won't give it up

Win 11 Pro 25H2, latest OS build. Started up for the second time today -- first time as usual -- and the taskbar and most all programs have all of a sudden turned black background, except for the central part of the screen in browsers. I went into Settings...>Color and changed them to light, but they won't hold, during the session or after reboot. What might be going on? The taskbar color is one of those things I don't pay close attention unless it changes, but I thought it had a transparent tone before this (transparency is on).