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NAME | SYNOPSIS | DESCRIPTION | CONSTANTS | VARIABLES | FUNCTIONS | RETURN VALUE | NOTES | EXTENSIONS | PORTABILITY | HISTORY | SEE ALSO | COLOPHON |
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curs_color(3X) Library calls curs_color(3X)
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, A_COLOR - manipulate
terminal colors with curses
#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);
/* macros */
int COLOR_PAIR(int n);
PAIR_NUMBER(int attr);
COLOR_BLACK
COLOR_RED
COLOR_GREEN
COLOR_YELLOW
COLOR_BLUE
COLOR_MAGENTA
COLOR_CYAN
COLOR_WHITE
A_COLOR
Overview
curses supports color attributes on terminals with that
capability. Call start_color (typically right after initscr(3X))
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(3X) or
wadd_wch(3X)
• window attributes, as from wattrset(3X) or wattr_set(3X)
• window background character attributes, as from wbkgdset(3X)
or wbkgrndset(3X)
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.
ISO 6429 and ECMA-48 define eight standard colors (also known as
“ANSI” colors). curses.h defines object-like macros COLOR_BLACK,
COLOR_RED, COLOR_GREEN, COLOR_YELLOW, COLOR_BLUE, COLOR_MAGENTA,
COLOR_CYAN, and COLOR_WHITE accordingly. curses assumes that
COLOR_BLACK is the default background color for all terminals.
ncurses offers an extension to override that assumption; see
assume_default_colors(3X). Some terminals support additional
colors that lack standard names.
A_COLOR is a bit mask that, when bitwise “and”-ed with a chtype,
extracts its color pair identifier.
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.
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(3X)).
• 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
has_colors returns TRUE if the terminal supports colors and FALSE
if it does not. initscr(3X) or newterm(3X) must be called first,
but start_color need not be. An application might call has_colors
to decide whether to use color or a video attribute like A_BOLD to
render text.
Color support in curses requires that the terminal type
description support the capabilities max_colors (colors),
max_pairs (pairs), and any of
• set_foreground (setf) and set_background (setb);
• set_a_foreground (setaf) and set_a_background (setab); or
• set_color_pair (scp).
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(3X)) 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(3X) routine, or to specify the use of
default colors (color number -1) if you first invoke the
use_default_colors(3X) 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.
can_change_color and has_colors return TRUE or FALSE. The other
functions return OK on success and ERR on failure.
In ncurses, functions returning an int recognize several error
conditions.
• All return ERR if the screen has not been initialized; see
initscr(3X) or newterm(3X).
• All except start_color return ERR if start_color has not been
called, or itself returned ERR.
• start_color returns ERR if it cannot allocate memory for its
color pair table.
• init_color returns ERR if the terminal type does not support
assignable color values; that is, if the initialize_color
(initc) capability is absent from its description.
• init_color returns ERR if any of its r, g, b arguments is
outside the range 0-1000 inclusive.
• init_pair, init_color, init_extended_pair,
init_extended_color, color_content, pair_content,
extended_color_content, and extended_pair_content return ERR
on attempts to use
• color identifiers outside the range 0-COLORS-1 inclusive,
the default colors extension notwithstanding, or
• color pair identifiers outside the range 0-COLOR_PAIRS-1
inclusive.
In ncurses, init_pair accepts negative foreground and background
color arguments to support its use_default_colors(3X) extension,
but only after the latter function has been called.
The assumption that COLOR_BLACK is the terminal's default
background color can be overridden using ncurses's
assume_default_colors(3X) extension.
In ncurses, each pointer passed to color_content and pair_content
can be null, in which case the library ignores it, permitting the
application to disregard unnecessary information.
In ncurses, each screen has a color activation flag, color
palette, color pair table, and associated COLORS and COLOR_PAIRS
values; start_color affects only the current screen. The SVr4 and
X/Open Curses interface was not really designed with this in mind;
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
curs_bkgd(3X).
Several caveats apply to IBM PC-compatible machines of the 80486
era and earlier with CGA/EGA/VGA video.
• COLOR_YELLOW was frequently converted, in the analog domain,
to a shade of brown if the intensity bit was not set. To get
yellow on such devices, one would combine COLOR_YELLOW with
the A_BOLD attribute.
• The A_BLINK attribute should in theory make the background
bright. This often fails to work, and even VGA controllers
for which it mostly works, such as those from 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 configurable on these devices (in
text mode).
The functions marked as extensions originated in ncurses, and are
not found in SVr4 curses, 4.4BSD curses, or any other previous
curses implementation.
Applications employing ncurses extensions should condition their
use on the visibility of the NCURSES_VERSION preprocessor macro.
X/Open Curses Issue 4 describes these functions. It specifies no
error conditions for them.
ncurses satisfies X/Open Curses's minimum maximums for COLORS and
COLOR_PAIRS.
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. ncurses provides extended versions of the
functions using short parameters, allowing applications to use
larger color and pair identifiers.
SVr4 curses returns ERR from pair_content if its pair argument was
not initialized using init_pairs, and from color_content if the
terminal does not support changing colors. ncurses does neither.
SVr3.2 (1987) introduced color support to curses with all of the
symbols in the synopsis above except those marked as extensions.
It reserved color pair 0 as the terminal's initial, “uncolored”
state, and limited the number of possible color pairs to 64,
because the color pair datum was encoded in six bits of a chtype.
SVr4 made only internal changes, such as moving the storage of
color state from the SCREEN structure (pointed to by SP) to the
TERMINAL structure (pointed to by cur_term).
Other curses implementations impose different limits on the number
of colors and color pairs.
• PCCurses (1987-1990) provided for only 8 colors (and therefore
required at most 8×8 = 64 color pairs).
• PDCurses (1992-present) inherited the 8-color limitation from
PCCurses, but changed this to 256 in version 2.5 (2001), and
widened its chtype from 16 to 32 bits.
• X/Open Curses (1992-present) specified a new structure type,
cchar_t, to store the character code, attribute flags, and
color pair identifier, allowing an increased range of color
pairs. It specifies a short as storing identifiers for colors
and color pairs, limiting portable values to 15 bits; negative
values are invalid in System V.
• ncurses (1992-present), in its non-wide-character
configuration, uses 8 bits of chtype for the color pair
identifier.
Version 5.3 (2002) offered a wide-character interface, but
encoded the color pair identifier with attributes in the
character type.
Since version 6 (2015), ncurses uses a separate int for the
color pair identifier in a cchar_t, introducing extension
functions to manage the wider type. When a color pair value
fits in 8 bits, ncurses permits color pair data to be
manipulated via the functions taking chtype arguments, even
when a curses window uses wide-character cells.
• NetBSD curses used 6 bits for the color pair identifier from
2000 (when it first added color support) until 2004. At that
point, NetBSD widened the color pair identifier to use 9 bits.
As of 2025, that size is unchanged. Like ncurses before
version 6, the NetBSD color pair datum is stored in the
attributes field of cchar_t, limiting the number of color
pairs.
curses(3X), curs_attr(3X), curs_initscr(3X), curs_variables(3X),
default_colors(3X)
This page is part of the ncurses (new curses) project.
Information about the project can be found at
⟨https://invisible-island.net/ncurses/ncurses.html⟩. If you have a
bug report for this manual page, send it to bug-ncurses@gnu.org.
This page was obtained from the tarball ncurses-6.6.tar.gz fetched
from ⟨https://ftp.gnu.org/gnu/ncurses/⟩ on 2026-01-16. If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for the
page, or you have corrections or improvements to the information
in this COLOPHON (which is not part of the original manual page),
send a mail to man-pages@man7.org
ncurses @NCURSES_MAJOR@.@NCU... 2025-08-23 curs_color(3X)
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HTML rendering created 2026-01-16 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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