Provided by: ncurses-doc_6.4+20240113-1ubuntu2_all 
NAME
start_color, has_colors, can_change_color, init_pair, init_color, init_extended_pair,
init_extended_color, color_content, pair_content, extended_color_content, extended_pair_content,
reset_color_pairs, COLOR_PAIR, PAIR_NUMBER, COLORS, COLOR_PAIRS, COLOR_BLACK, COLOR_RED, COLOR_GREEN,
COLOR_YELLOW, COLOR_BLUE, COLOR_MAGENTA, COLOR_CYAN, COLOR_WHITE - manipulate terminal colors with curses
SYNOPSIS
#include <curses.h>
/* variables */
int COLOR_PAIRS;
int COLORS;
int start_color(void);
bool has_colors(void);
bool can_change_color(void);
int init_pair(short pair, short f, short b);
int init_color(short color, short r, short g, short b);
/* extensions */
int init_extended_pair(int pair, int f, int b);
int init_extended_color(int color, int r, int g, int b);
int color_content(short color, short *r, short *g, short *b);
int pair_content(short pair, short *f, short *b);
/* extensions */
int extended_color_content(int color, int *r, int *g, int *b);
int extended_pair_content(int pair, int *f, int *b);
/* extension */
void reset_color_pairs(void);
int COLOR_PAIR(int n);
PAIR_NUMBER(int attr);
DESCRIPTION
Overview
curses supports color attributes on terminals with that capability. Call start_color (typically right
after initscr(3NCURSES)) to enable this feature. Colors are always used in pairs. A color pair couples
a foreground color for characters with a background color for the blank field on which characters are
rendered. init_pair initializes a color pair. The macro COLOR_PAIR(n) can then convert the pair to a
video attribute.
If a terminal has the relevant capability, init_color permits (re)definition of a color. has_colors and
can_change_color return TRUE or FALSE, depending on whether the terminal has color capability and whether
the programmer can change the colors. color_content permits extraction of the red, green, and blue
components of an initialized color. pair_content permits discovery of a color pair's current definition.
Rendering
curses combines the following data to render a character cell. Any of them can include color
information.
• curses character attributes, as from waddch(3NCURSES) or wadd_wch(3NCURSES)
• window attributes, as from wattrset(3NCURSES) or wattr_set(3NCURSES)
• window background character attributes, as from wbkgdset(3NCURSES) or wbkgrndset(3NCURSES)
Per-character and window attributes are usually set through a function parameter containing attributes
including a color pair value. Some functions, such as wattr_set, use a separate color pair number
parameter.
The background character is a special case: it includes a character code, just as if it were passed to
waddch.
The curses library does the actual work of combining these color pairs in an internal function called
from waddch:
• If the parameter passed to waddch is blank, and it uses the special color pair 0,
• curses next checks the window attribute.
• If the window attribute does not use color pair 0, curses uses the color pair from the window
attribute.
• Otherwise, curses uses the background character.
• If the parameter passed to waddch is not blank, or it does not use the special color pair 0, curses
prefers the color pair from the parameter, if it is nonzero. Otherwise, it tries the window
attribute next, and finally the background character.
Some curses functions such as wprintw call waddch. Those do not combine its parameter with a color pair.
Consequently those calls use only the window attribute or the background character.
CONSTANTS
In <curses.h> the following macros are defined. These are the standard colors (ISO-6429). curses also
assumes that COLOR_BLACK is the default background color for all terminals.
COLOR_BLACK
COLOR_RED
COLOR_GREEN
COLOR_YELLOW
COLOR_BLUE
COLOR_MAGENTA
COLOR_CYAN
COLOR_WHITE
Some terminals support more than the eight (8) “ANSI” colors. There are no standard names for those
additional colors.
VARIABLES
COLORS
is initialized by start_color to the maximum number of colors the terminal can support.
COLOR_PAIRS
is initialized by start_color to the maximum number of color pairs the terminal can support. Often, its
value is the product COLORS × COLORS, but this is not always true.
• A few terminals use the HLS color space (see start_color below), ignoring this rule; and
• terminals supporting a large number of colors are limited to the number of color pairs that a signed
short value can represent.
FUNCTIONS
start_color
The start_color routine requires no arguments. It must be called if the programmer wants to use colors,
and before any other color manipulation routine is called. It is good practice to call this routine
right after initscr. start_color does this:
• It initializes two global variables, COLORS and COLOR_PAIRS (respectively defining the maximum number
of colors and color pairs the terminal can support).
• It initializes the special color pair 0 to the default foreground and background colors. No other
color pairs are initialized.
• It restores the colors on the terminal to the values they had when the terminal was just turned on.
• If the terminal supports the initc (initialize_color) capability, start_color initializes its
internal table representing the red, green, and blue components of the color palette.
The components depend on whether the terminal uses CGA (aka “ANSI”) or HLS (i.e., the hls
(hue_lightness_saturation) capability is set). The table is initialized first for eight basic colors
(black, red, green, yellow, blue, magenta, cyan, and white), using weights that depend upon the
CGA/HLS choice. For “ANSI” colors the weights are 680 or 0 depending on whether the corresponding
red, green, or blue component is used or not. That permits using 1000 to represent bold/bright
colors. After the initial eight colors (if the terminal supports more than eight colors) the
components are initialized using the same pattern, but with weights of 1000. SVr4 uses a similar
scheme, but uses 1000 for the components of the initial eight colors.
start_color does not attempt to set the terminal's color palette to match its built-in table. An
application may use init_color to alter the internal table along with the terminal's color.
These limits apply to color values and color pairs. Values outside these limits are not valid, and may
result in a runtime error:
• COLORS corresponds to the terminal database's max_colors capability, (see terminfo(5)).
• color values are expected to be in the range 0 to COLORS-1, inclusive (including 0 and COLORS-1).
• a special color value -1 is used in certain extended functions to denote the default color (see
use_default_colors(3NCURSES)).
• COLOR_PAIRS corresponds to the terminal database's max_pairs capability, (see terminfo(5)).
• valid color pair values are in the range 1 to COLOR_PAIRS-1, inclusive.
• color pair 0 is special; it denotes “no color”.
Color pair 0 is assumed to be white on black, but is actually whatever the terminal implements before
color is initialized. It cannot be modified by the application.
has_colors
The has_colors routine requires no arguments. It returns TRUE if the terminal can manipulate colors;
otherwise, it returns FALSE. This routine facilitates writing terminal-independent programs. For
example, a programmer can use it to decide whether to use color or some other video attribute.
can_change_color
The can_change_color routine requires no arguments. It returns TRUE if the terminal supports colors and
can change their definitions; other, it returns FALSE. This routine facilitates writing terminal-
independent programs.
init_pair
The init_pair routine changes the definition of a color pair. It takes three arguments: the number of
the color pair to be changed, the foreground color number, and the background color number. For portable
applications:
• The first argument must be a valid color pair value. If default colors are used (see
use_default_colors(3NCURSES)) the upper limit is adjusted to allow for extra pairs which use a
default color in foreground and/or background.
• The second and third arguments must be valid color values.
If the color pair was previously initialized, the screen is refreshed and all occurrences of that color
pair are changed to the new definition.
As an extension, ncurses allows you to set color pair 0 via the assume_default_colors(3NCURSES) routine,
or to specify the use of default colors (color number -1) if you first invoke the
use_default_colors(3NCURSES) routine.
init_extended_pair
Because init_pair uses signed shorts for its parameters, that limits color pairs and color-values to
32767 on modern hardware. The extension init_extended_pair uses ints for the color pair and color-value,
allowing a larger number of colors to be supported.
init_color
The init_color routine changes the definition of a color. It takes four arguments: the number of the
color to be changed followed by three RGB values (for the amounts of red, green, and blue components).
• The first argument must be a valid color value; default colors are not allowed here. (See the
section Colors for the default color index.)
• Each of the last three arguments must be a value in the range 0 through 1000.
When init_color is used, all occurrences of that color on the screen immediately change to the new
definition.
init_extended_color
Because init_color uses signed shorts for its parameters, that limits color-values and their red, green,
and blue components to 32767 on modern hardware. The extension init_extended_color uses ints for the
color value and for setting the red, green, and blue components, allowing a larger number of colors to be
supported.
color_content
The color_content routine gives programmers a way to find the intensity of the red, green, and blue (RGB)
components in a color. It requires four arguments: the color number, and three addresses of shorts for
storing the information about the amounts of red, green, and blue components in the given color.
• The first argument must be a valid color value, i.e., 0 through COLORS-1, inclusive.
• The values that are stored at the addresses pointed to by the last three arguments are in the range 0
(no component) through 1000 (maximum amount of component), inclusive.
extended_color_content
Because color_content uses signed shorts for its parameters, that limits color-values and their red,
green, and blue components to 32767 on modern hardware. The extension extended_color_content uses ints
for the color value and for returning the red, green, and blue components, allowing a larger number of
colors to be supported.
pair_content
The pair_content routine allows programmers to find out what colors a given color pair consists of. It
requires three arguments: the color pair number, and two addresses of shorts for storing the foreground
and the background color numbers.
• The first argument must be a valid color value, i.e., in the range 1 through COLOR_PAIRS-1,
inclusive.
• The values that are stored at the addresses pointed to by the second and third arguments are in the
range 0 through COLORS, inclusive.
extended_pair_content
Because pair_content uses signed shorts for its parameters, that limits color pair and color-values to
32767 on modern hardware. The extension extended_pair_content uses ints for the color pair and for
returning the foreground and background colors, allowing a larger number of colors to be supported.
reset_color_pairs
The extension reset_color_pairs tells ncurses to discard all of the color pair information which was set
with init_pair. It also touches the current- and standard-screens, allowing an application to switch
color palettes rapidly.
COLOR_PAIR
COLOR_PAIR(n) converts a color pair number to an attribute. Attributes can hold color pairs in the range
0 to 255. If you need a color pair larger than that, you must use functions such as attr_set (which pass
the color pair as a separate parameter) rather than the legacy functions such as attrset.
PAIR_NUMBER
PAIR_NUMBER(attr) extracts the color information from its attr parameter and returns it as a color pair
number; it is the inverse operation of COLOR_PAIR.
RETURN VALUE
The routines can_change_color and has_colors return TRUE or FALSE.
All other routines return the integer ERR upon failure and an OK (SVr4 specifies only “an integer value
other than ERR”) upon successful completion.
X/Open defines no error conditions. SVr4 does document some error conditions which apply in general:
• This implementation will return ERR on attempts to use color values outside the range 0 to COLORS-1
(except for the default colors extension), or use color pairs outside the range 0 to COLOR_PAIRS-1.
Color values used in init_color must be in the range 0 to 1000.
An error is returned from all functions if the terminal has not been initialized.
An error is returned from secondary functions such as init_pair if start_color was not called.
• SVr4 does much the same, except that it returns ERR from pair_content if the pair was not initialized
using init_pairs and it returns ERR from color_content if the terminal does not support changing
colors.
This implementation does not return ERR for either case.
Specific functions make additional checks:
init_color
returns an error if the terminal does not support this feature, e.g., if the initialize_color
capability is absent from the terminal description.
start_color
returns an error if the color table cannot be allocated.
NOTES
In the ncurses implementation, there is a separate color activation flag, color palette, color pairs
table, and associated COLORS and COLOR_PAIRS counts for each screen; the start_color function only
affects the current screen. The SVr4/XSI interface is not really designed with this in mind, and
historical implementations may use a single shared color palette.
Setting an implicit background color via a color pair affects only character cells that a character write
operation explicitly touches. To change the background color used when parts of a window are blanked by
erasing or scrolling operations, see bkgd(3NCURSES).
Several caveats apply on older x86 machines (e.g., i386, i486) with VGA-compatible graphics:
• COLOR_YELLOW is actually brown. To get yellow, use COLOR_YELLOW combined with the A_BOLD attribute.
• The A_BLINK attribute should in theory cause the background to go bright. This often fails to work,
and even some cards for which it mostly works (such as the Paradise and compatibles) do the wrong
thing when you try to set a bright “yellow” background (you get a blinking yellow foreground
instead).
• Color RGB values are not settable.
EXTENSIONS
The functions marked as extensions were designed for ncurses(3NCURSES), and are not found in SVr4 curses,
4.4BSD curses, or any other previous curses implementation.
PORTABILITY
Applications employing ncurses extensions should condition their use on the visibility of the
NCURSES_VERSION preprocessor macro.
This implementation satisfies XSI Curses's minimum maximums for COLORS and COLOR_PAIRS.
The init_pair routine accepts negative values of foreground and background color to support the
use_default_colors(3NCURSES) extension, but only if that routine has been first invoked.
The assumption that COLOR_BLACK is the default background color for all terminals can be modified using
the assume_default_colors(3NCURSES) extension.
This implementation checks the pointers, e.g., for the values returned by color_content and pair_content,
and will treat those as optional parameters when null.
X/Open Curses does not specify a limit for the number of colors and color pairs which a terminal can
support. However, in its use of short for the parameters, it carries over SVr4's implementation detail
for the compiled terminfo database, which uses signed 16-bit numbers. This implementation provides
extended versions of those functions which use short parameters, allowing applications to use larger
color- and pair-numbers.
The reset_color_pairs function is an extension of ncurses.
HISTORY
SVr3.2 introduced color support to curses in 1987.
SVr4 made internal changes, e.g., moving the storage for the color state from SP (the SCREEN structure)
to cur_term (the TERMINAL structure), but provided the same set of library functions.
SVr4 curses limits the number of color pairs to 64, reserving color pair zero (0) as the terminal's
initial uncolored state. This limit arises because the color pair information is a bitfield in the
chtype data type (denoted by A_COLOR).
Other implementations of curses had different limits:
• PCCurses (1987-1990) provided for only eight (8) colors.
• PDCurses (1992-present) inherited the 8-color limitation from PCCurses, but changed this to 256 in
version 2.5 (2001), along with changing chtype from 16-bits to 32-bits.
• X/Open Curses (1992-present) added a new structure cchar_t to store the character, attributes and
color pair values, allowing increased range of color pairs. Both color pairs and color-values used a
signed short, limiting values to 15 bits.
• ncurses (1992-present) uses eight bits for A_COLOR in chtype values.
Version 5.3 provided a wide-character interface (2002), but left color pairs as part of the
attributes-field.
Since version 6 (2015), ncurses uses a separate int for color pairs in the cchar_t values. When
those color pair values fit in 8 bits, ncurses allows color pairs to be manipulated via the functions
using chtype values.
• NetBSD curses used 6 bits from 2000 (when colors were first supported) until 2004. At that point,
NetBSD changed to use 10 bits. As of 2021, that size is unchanged. Like ncurses before version 6,
the NetBSD color pair information is stored in the attributes field of cchar_t, limiting the number
of color pairs by the size of the bitfield.
SEE ALSO
ncurses(3NCURSES), attr(3NCURSES), initscr(3NCURSES), curses_variables(3NCURSES),
default_colors(3NCURSES)
ncurses 6.4 2023-12-30 color(3NCURSES)