assume_default_colors() functions are extensions to the curses library.
They are used with terminals that support ISO 6429 color, or equivalent.
These terminals allow the application to reset color to an unspecified
default value (e.g., with SGR 39 or SGR 49).
Applications that paint a colored background over the whole screen
do not take advantage of SGR 39 and SGR 49.
Some applications are designed to work with the default background,
using colors only for text.
For example, there are several implementations of the ls program
which use colors to denote different file types or permissions.
These "color ls" programs do not necessarily modify the background color,
typically using only the setaf terminfo capability to set the
Full-screen applications that use default colors can achieve similar
The first function,
use_default_colors() tells the curses library to assign terminal default
foreground/background colors to color number -1. So init_pair(x,COLOR_RED,-1)
will initialize pair x as red on default background and init_pair(x,-1,COLOR_BLUE) will
initialize pair x as default foreground on blue.
assume_default_colors() is a refinement which tells which colors to paint for color pair 0.
This function recognizes a special color number -1,
which denotes the default terminal color.
The following are equivalent:
These are ncurses extensions.
For other curses implementations, color
number -1 does not mean anything, just as for ncurses before a
successful call of use_default_colors() or assume_default_colors().
Other curses implementations do not allow an application to modify color pair 0.
They assume that the background is COLOR_BLACK,
but do not ensure that the color pair 0 is painted to match the
If your application does not use either
assume_default_colors() ncurses will paint a white foreground (text) with black background
for color pair 0.
Associated with this extension, the init_pair function accepts
negative arguments to specify default foreground or background colors.
The use_default_colors() function was added to support ded.
This is a full-screen application which uses curses to manage only part
of the screen. The bottom portion of the screen, which is of adjustable
size, is left uncolored to display the results from shell commands.
The top portion of the screen colors filenames using a scheme like the
"color ls" programs.
Attempting to manage the background color of the screen for this application
would give unsatisfactory results for a variety of reasons.
This extension was devised after
noting that color xterm (and similar programs) provides a background color
which does not necessarily correspond to any of the ANSI colors.
While a special terminfo entry could be constructed using nine colors,
there was no mechanism provided within curses to account for the related
orig_pair and back_color_erase capabilities.
The assume_default_colors() function was added to solve
a different problem: support for applications which would use
environment variables and other configuration to bypass curses
notion of the terminals default colors, setting specific values.