plain-vanilla

[ pleyn-vuh-nil-uh ]
/ ˈpleɪn vəˈnɪl ə /

adjective Informal.

having no embellishments, extra equipment, elaborate packaging, etc.; plain; simple; down-to-earth: I want a plain-vanilla car without a lot of chrome trim.

Origin of plain-vanilla

in allusion to vanilla ice cream, taken to be the most basic flavor