Variable: frame-background-mode
frame-background-mode is a customizable variable defined in
frame.el.gz.
Value
nil
Documentation
The brightness of the background.
Set this to the symbol dark if your background color is dark,
light if your background is light, or nil (automatic by default)
if you want Emacs to examine the brightness for you.
If you change this without using customize, you should use
frame-set-background-mode to update existing frames;
e.g. (mapc 'frame-set-background-mode (frame-list)).
Source Code
;; Defined in /usr/src/emacs/lisp/frame.el.gz
;;;; Background mode.
(defcustom frame-background-mode nil
"The brightness of the background.
Set this to the symbol `dark' if your background color is dark,
`light' if your background is light, or nil (automatic by default)
if you want Emacs to examine the brightness for you.
If you change this without using customize, you should use
`frame-set-background-mode' to update existing frames;
e.g. (mapc \\='frame-set-background-mode (frame-list))."
:group 'faces
:set #'(lambda (var value)
(set-default var value)
(mapc #'frame-set-background-mode (frame-list)))
:initialize #'custom-initialize-changed
:type '(choice (const dark)
(const light)
(const :tag "automatic" nil)))