+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 \fBls\fP 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 \fIsetaf\fP terminfo capability to set the
+foreground color.
+Full-screen applications that use default colors can achieve similar
+visual effects.
+.PP
+The first function,
+.I 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.
+.PP
+The other,
+.I 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.
+.PP
+The following are equivalent:
+.RS
+.br
+.I use_default_colors();
+.br
+.I assume_default_colors(-1,-1);
+.RE
+.PP
+These are ncurses extensions.
+For other curses implementations, color
+number -1 does not mean anything, just as for ncurses before a
+successful call of \fIuse_default_colors()\fP or \fIassume_default_colors()\fP.
+.PP
+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
+assumption.
+If your application does not use either
+.I use_default_colors()
+or
+.I assume_default_colors()
+ncurses will paint a white foreground (text) with black background
+for color pair 0.