mode-line-in-non-selected-windows

mode-line-in-non-selected-windows is a variable defined in `C source code'.
Its value is

t

Documentation:
Non-nil means to use `mode-line-inactive' face in non-selected windows.
If the minibuffer is active, the `minibuffer-scroll-window' mode line
is displayed in the `mode-line' face.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 22.1 of Emacs.