Problem solved. Not Windows related at all, but tied to DELL monitor. Go to Dell Display Manager. There is a choice of "Auto" or "Manual". In "Auto", the monitor settings "Multimedia, Standard, Movie, etc." will show up in the upper left monitor screen. Just switch to "Manual" to remove this feature.
Several clicks need to be made to change this, so it didn't happen by accident. Still wondering how it changed by itself.