https://docs.oracle.com/cd/E86824_01/html/E54767/getbkgd-3xcurses.html
getbkgd - man pages section 3: Curses Library Functions
bkgd , bkgdset , getbkgd , wbkgd , wbkgdset - set or get the background character (and rendition) of window
man pagessectioncurseslibraryfunctions