GNU Emacs Lisp Reference Manual

35.12: Inverse Video

User Option: inverse-video

This variable controls whether Emacs uses inverse video for all text on the screen. Non-nil means yes, nil means no. The default is nil.

User Option: mode-line-inverse-video

This variable controls the use of inverse video for mode lines. If it is non-nil, then mode lines are displayed in inverse video. Otherwise, mode lines are displayed normally, just like text. The default is t.

For X window frames, this displays mode lines using the face named modeline, which is normally the inverse of the default face unless you change it.