curs\_color(3X) Library calls curs\_color(3X)

# [NAME](#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**, **A\_COLOR** - manipulate terminal colors with *curses*

# [SYNOPSIS](#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 index, short r, short g, short b);
/* extensions */
int init_extended_pair(int pair, int f, int b);
int init_extended_color(int index, int r, int g, int b);
```

```
int color_content(short index, short *r, short *g, short *b);
int pair_content(short pair, short *f, short *b);
/* extensions */
int extended_color_content(int index, 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
```

# [DESCRIPTION](#DESCRIPTION)

*curses* supports color rendering on terminals with applicable capabilities. Once the library has initialized the terminal, **has\_colors** tells an application whether that terminal type has color capability. If it does, calling **start\_color** enables the feature. (See section “NOTES” below regarding [**ripoffline**(3X)](/man/os/ncurses/ripoffline.3X).)

When applying colors to a *curses* window, the library manages them in pairs. A *color pair* couples a foreground color applied to the visible strokes of a glyph with a background color for the field in the character cell within which the glyph appears. Configure at least one color pair to use the color feature. **init\_pair** initializes a color pair identifier, whose value you select, from a pair of *color indices,* foreground and background. Each index represents a color. X/Open Curses standardizes, and a *curses* library defines, a small set of color indices; see section “MACROS” below. The macro **COLOR\_PAIR(*n*)** converts a pair *n* thus initialized to the value required to encode it in a *chtype* or *attr\_t*. Another macro, **PAIR\_NUMBER(*n*)** conversely extracts a color pair identifier from variables of those data types. **pair\_content** permits discovery of a color pair's current definition. **color\_content** extracts the red, green, and blue components of the color using the given index.

**can\_change\_color** tells an application whether the terminal type permits (re)definition of a color. If it does, you can call **init\_color** to update the specified color index to use red, green, and blue components of your choice.

Subsection “Color Handling” of [**terminfo**(5)](/man/os/ncurses/terminfo.5) describes the capabilities that terminal types use to manage color.

Passing a *curses* function a color index outside the range **0** to **COLORS-1**, or a color pair identifier outside the range **0** to **COLOR\_PAIRS-1** may result in a runtime error. **COLORS** corresponds to the terminal type's **max\_colors** (**colors**) capability, and **COLOR\_PAIRS** to **max\_pairs** (**pairs**). *ncurses* permits specification of a color index of **-1** in certain extended functions to select a *default color*; see [**use\_default\_colors**(3X)](/man/os/ncurses/use_default_colors.3X).

Color pair **0** is special; it denotes “no color”, meaning the terminal's (typically monochrome) power-up default fore- and background.

For each screen, *ncurses* maintains a *color palette* that maps color indices into the RGB (red, green, blue) color space.

# [VARIABLES](#VARIABLES)

## [COLORS](#COLORS)

is initialized by **start\_color** to the maximum number of colors the terminal can support.

## [COLOR\_PAIRS](#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, ignoring this rule; and
- while a terminal type may support many colors, a portable *curses* application is limited to the number of distinct color indices and color pair identifiers that a *signed short* value can represent.

# [FUNCTIONS](#FUNCTIONS)

## [has\_colors](#has_colors)

**has\_colors** returns **TRUE** if the terminal supports colors and **FALSE** if it does not. [**initscr**(3X)](/man/os/ncurses/initscr.3X) or [**newterm**(3X)](/man/os/ncurses/newterm.3X) must be called first, but **start\_color** need not be. An application might call **has\_colors** to inform its decision whether to use color or a video attribute like **A\_BOLD** to render text.

## [start\_color](#start_color)

If your application requires color, call **start\_color** before any other color manipulation function. As a rule, do so immediately after **initscr**. If the terminal type supports color, **start\_color**:

- initializes the two global variables, **COLORS** and **COLOR\_PAIRS**, described above;
- initializes (only) the color pair **0** to the terminal type's power-up foreground and background colors (but see the *ncurses* extension [**use\_default\_colors**(3X)](/man/os/ncurses/use_default_colors.3X));
- initializes the color palette; and
- selects color pair **0**.

**start\_color** sets up the color palette for the eight colors named by the X/Open Curses standard (see section “CONSTANTS” above) applying weights appropriate to the color space. *curses* does not attempt to initialize the color palette to match a terminal type's power-up configuration. See section “NOTES” below.

Calling **start\_color** again after it has returned **OK** does nothing.

## [init\_pair](#init_pair)

(Re-)define a color pair with **init\_pair**, which takes three arguments: the color pair identifier to be updated, a foreground color index, and a background color index. A portable application restricts these argument values to the valid ranges stated above. If the application uses *ncurses*'s default color extension (see below), the library adjusts the upper limit to allow for extra pairs that use a default color in the foreground and/or background.

If a color pair was previously defined, **init\_pair** causes a refresh of the entire screen, and all occurrences of that color pair change to use its new definition. *ncurses* suppresses this refresh if the color pair's new color indices are the same as the old.

*ncurses* extensions allow you to update color pair **0** via [**assume\_default\_colors**(3X)](/man/os/ncurses/assume_default_colors.3X), and to access the terminal's default colors as color index **-1** if you first call [**use\_default\_colors**(3X)](/man/os/ncurses/use_default_colors.3X).

## [init\_extended\_pair](#init_extended_pair)

Because **init\_pair** uses signed *short*s for its parameters, its color pair identifiers and color indices are limited to 32767 even for terminal types that are much more capable. This *ncurses* extension uses *int*s instead, expanding their range.

## [pair\_content](#pair_content)

An application can discover the color index assignments of a color pair with **pair\_content**. Its first argument is the color pair identifier of interest, and the remaining two are each a pointer to *short* that the function populates with the foreground and background color indices, respectively.

## [extended\_pair\_content](#extended_pair_content)

Because **pair\_content** uses signed *short*s for its parameters, its color pair identifiers and color indices are limited to 32767 even for terminal types that are much more capable. This *ncurses* extension uses *int*s instead, expanding their range.

## [reset\_color\_pairs](#reset_color_pairs)

This *ncurses* extension directs the library to discard all color pair assignments configured by application calls of **init\_pair** and **init\_extended\_pair**. It furthermore marks the entire screen as requiring refresh; an application can thus easily reconfigure its color scheme by subsequently initializing as many color pairs as required.

## [can\_change\_color](#can_change_color)

**can\_change\_color** returns **TRUE** if the terminal supports colors and can change their mappings, and **FALSE** if it does not.

## [init\_color](#init_color)

Change a color's mapping (definition) by supplying this function four arguments: the color index; and red, green, and blue color channel values in the range 0-1000.

If the color index is in use in a color pair on the screen, all occurrences of it change to use its new definition. No [**refresh**(3X)](/man/os/ncurses/refresh.3X) is necessary.

## [init\_extended\_color](#init_extended_color)

Because **init\_color** uses signed *short*s for its parameters, the maximum value of its color index argument is limited to 32767 even for terminal types that are much more capable. (The range of valid RGB channel values remains 0-1000.) This *ncurses* extension uses *int*s instead, expanding the range of permissible color indices.

If the color index is in use in a color pair on the screen, all occurrences of it change to use its new definition. No [**refresh**(3X)](/man/os/ncurses/refresh.3X) is necessary.

## [color\_content](#color_content)

An application can query a color index's location in RGB space by calling **color\_content**. The library stores the color channel values corresponding to the specified color index in the *red*, *green*, and *blue* pointer-to-*short* arguments.

## [extended\_color\_content](#extended_color_content)

Because **color\_content** uses signed *short*s for its parameters, the maximum value of its color index argument is limited to 32767 even for terminal types that are much more capable. This *ncurses* extension uses *int*s instead, expanding the range of permissible color indices.

# [MACROS](#MACROS)

ISO 6429 and ECMA-48 define eight standard colors (known inaccurately as “ANSI” colors), to which X/Open Curses assigns symbolic names as object-like macros **COLOR\_BLACK**, **COLOR\_RED**, **COLOR\_GREEN**, **COLOR\_YELLOW**, **COLOR\_BLUE**, **COLOR\_MAGENTA**, **COLOR\_CYAN**, and **COLOR\_WHITE**. *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)](/man/os/ncurses/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. X/Open Curses mandates the provision of two function-like macros. They have no application in the wide-character API of *curses*.

## [COLOR\_PAIR](#COLOR_PAIR)

**COLOR\_PAIR(n)** replaces color pair identifier *n* with its encoded value appropriate for use in a *chtype*. Such values have a limited, implementation-dependent range. Non-wide API functions such as [**attrset**(3X)](/man/os/ncurses/attrset.3X) cannot handle larger color pair identifiers than this. A portable application checks that *n*'s value is less than *COLOR\_PAIRS* before employing this macro on it. If you need to transform a larger color pair identifier, you must use the wide API and call, for example, [**attr\_set**(3X)](/man/os/ncurses/attr_set.3X), which passes the color pair identifier as a parameter separate from the attributes.

## [PAIR\_NUMBER](#PAIR_NUMBER)

**PAIR\_NUMBER(n)** replaces its *chtype* or *attr\_t* argument *n* with the color pair identifier encoded within it.

**COLOR\_PAIR()** and **PAIR\_NUMBER()** are inverse operations.

# [RETURN VALUE](#RETURN_VALUE)

**can\_change\_color** and **has\_colors** return **TRUE** or **FALSE**. The other functions return **OK** on success and **ERR** on failure.

In *ncurses*, color manipulation functions returning an *int* recognize several error conditions.

- All return **ERR** if the screen has not been initialized; see [**initscr**(3X)](/man/os/ncurses/initscr.3X) or [**newterm**(3X)](/man/os/ncurses/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

<!--THE END-->

- 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.

# [NOTES](#NOTES)

X/Open Curses says nothing about how the standard colors are to be configured in a color space. *ncurses* initializes a screen's color palette such that, in the RGB color space, each channel of the eight standard colors has a value of either **680** or **0**. If the terminal type supports at least 16 colors, this configuration aids an application to support a terminal type with only one typeface to simulate bold text with “bright” colors. With appropriate configuration of the bright color pairs by the application, increasing nonzero channel values to **1000**, this scheme suffices to approximate the 16 colors of IBM CGA text mode video and the power-up configuration of the DEC VT525. SVr4 *curses* instead assigns values of **1000** to the nonzero color channel values of the eight standard colors.

Setting a background color via a color pair identifier 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**(3X)](/man/os/ncurses/bkgd.3X) (wide-character API users: [**bkgrnd**(3X)](/man/os/ncurses/bkgrnd.3X)).

Windows created by [**ripoffline**(3X)](/man/os/ncurses/ripoffline.3X) do not inherit color pair configuration applied to *stdscr*; they must be configured independently.

In *ncurses*, **init\_pair** accepts negative foreground and background color arguments to support its [**use\_default\_colors**(3X)](/man/os/ncurses/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)](/man/os/ncurses/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 *curses* interface, standardized by X/Open Curses, was not designed with distinguishable screens clearly in mind; historical implementations may use a single shared color palette for all screens the library manages.

Several caveats apply to emulation of the CGA/EGA/VGA video of IBM PC-compatible machines of the 80486 era and earlier.

- **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).

## [Why This Color Model?](#Why_This_Color_Model?)

A programmer new to *curses* may wonder why the library works with pairs of indexed colors instead of “direct” foreground and background RGB triples. The answer lies in the limited bandwidth between terminals and their time-sharing host machines. In the 1980s, a 9600bps serial link was considered fast. That speed typically corresponded to a data rate of 960 bytes per second. Using a single-byte character encoding, refreshing an 80×24 terminal screen took two full seconds. In other words, such a terminal refreshing its entire screen contents rendered half a frame per second. Adding data to each character cell necessary for the “direct” color model at 8 bits per color channel would add 6 bytes to every character cell, extending the full-screen refresh time to 14 seconds. Even a pair of 8-bit color values would triple the refresh time.

Moreover, the vast majority of *curses* applications do not demand a wide gamut of colors. Even a colorful application like the game [**nethack**(6)](/man/os/ncurses/nethack.6) renders most of its interface in monochrome by default. A text user interface employing the [**form**(3X)](/man/os/ncurses/form.3X) or [**menu**(3X)](/man/os/ncurses/menu.3X) libraries often uses fewer than ten distinct colors at any one time. Thus, small integers suffice both to index individual colors and to pair them. Typically, each color pair is assigned to a type of user interface element, like a button or scroll bar control. Further, in the original SVr3.2 *curses* implementation of color and today still in *ncurses*'s non-wide library, *chtype* affords few bits for encoding of the color pair identifier.

Even in the common modern scenario where a terminal emulator runs on the same host as the *curses* application, and available bandwidth is limited only by the speed of the system bus, efficient encoding of character cell data aids performance by minimizing the copies to and from the kernel's memory space by use of the pseudoterminal (pty) system interface. For example, in the Linux 7.2 kernel, the pty buffer size is 4 KiB, ensuring a CPU mode switch every time it fills up. Parsimonious data management also reduces memory cache pressure.

# [EXTENSIONS](#EXTENSIONS)

The functions marked as extensions originated in *ncurses*, and are not found in SVr4 *curses*, 4.4BSD *curses*, or any other previous *curses* implementation.

# [PORTABILITY](#PORTABILITY)

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*.

*ncurses* does not refresh the screen if **init\_pair** is used to no effect on an existing color pair.

X/Open Curses does not specify a limit for the number of color indices and color pair identifiers 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 *int* parameters, allowing applications to use larger index 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.

# [HISTORY](#HISTORY)

SVr3.2 (1988) 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 (1989) 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 color indices and color pairs.

- *PCCurses* (1987-1990) provided for only 8 color indices (and therefore permitted at most 8×8 = 64 color pairs).
- *PDCurses* (1992-present) initially inherited the 8-color limitation from *PCCurses*, but increased it to 256 in version 2.5 (2001), and widened its *chtype* from 16 to 32 bits.
- X/Open Curses (1992-present) specified a new integral type, *attr\_t*, storing rendering attributes (see [**attr\_on**(3X)](/man/os/ncurses/attr_on.3X)) and a color pair identifier, and a new structure type, *cchar\_t*, to store a sequence of wide character codes separately from the character cell's attributes and color pair, allowing an increased range of color pairs. The standard specifies *attr\_t* as a *short*, 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) introduced 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*, adding extension functions to manage the wider type. When a color pair identifier fits in 8 bits, *ncurses* permits manipulation of color pair identifiers with 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 identifier is stored in the attributes field of *cchar\_t*, limiting the number of color pairs.

*ncurses* 6.1 (2018) introduced *init\_extended\_pair*, *init\_extended\_color*, *extended\_pair\_content*, *extended\_color\_content*, and *reset\_color\_pairs*.

# [SEE ALSO](#SEE_ALSO)

[**curses**(3X)](/man/os/ncurses/curses.3X), [**curs\_attr**(3X)](/man/os/ncurses/curs_attr.3X), [**curs\_initscr**(3X)](/man/os/ncurses/curs_initscr.3X), [**curs\_variables**(3X)](/man/os/ncurses/curs_variables.3X), [**default\_colors**(3X)](/man/os/ncurses/default_colors.3X)

2026-09-19 ncurses 6.6

---

Document: init_extended_color(3x) from ncurses 6.6.20261010-r0 (Chainguard OS)
Source: https://github.com/ThomasDickey/ncurses-snapshots