5.21 Colors

GNU troff supports color output with a variety of color spaces and up to 16 bits per channel. Some devices, particularly terminals, may be more limited. When color support is enabled, two colors are current at any given time: the stroke color, with which glyphs, rules (lines), and geometric objects like circles and polygons are drawn, and the fill color, which can be used to paint the interior of a closed geometric figure.

Request: .color [n]

Register: \n[.color]

If n is missing or non-zero, enable the output of color-related device-independent output commands (this is the default); otherwise, disable them. This request sets a global flag; it does not produce an input token (see Gtroff Internals).

The read-only register .color is 1 if colors are enabled, 0 otherwise.

Color can also be disabled with the -c command-line option.

Request: .defcolor ident scheme color-component …

Define a color named ident. scheme selects a color space and determines the quantity of required color-components; it must be one of ‘rgb’ (three components), ‘cmy’ (three), ‘cmyk’ (four), or ‘gray’ (one). ‘grey’ is accepted as a synonym of ‘gray’. The color components can be encoded as a single hexadecimal value starting with ‘#’ or ‘##’. The former indicates that each component is in the range 0–255 (0–FF), the latter the range 0–65,535 (0–FFFF).

.defcolor half gray #7f
.defcolor pink rgb #FFC0CB
.defcolor magenta rgb  ##ffff0000ffff

Alternatively, each color component can be specified as a decimal fraction in the range 0–1, interpreted using a default scaling unit of f, which multiplies its value by 65,536 (but clamps it at 65,535).

.defcolor gray50 rgb 0.5 0.5 0.5
.defcolor darkgreen rgb 0.1f 0.5f 0.2f

Each output device has a color named ‘default’, which cannot be redefined. A device’s default stroke and fill colors are not necessarily the same. For the dvi, html, pdf, ps, and xhtml output devices, GNU troff automatically loads a macro file defining many color names at startup. By the same mechanism, the devices supported by grotty recognize the eight standard ISO 6429/EMCA-48 color names.⁸⁶

Request: .gcolor [color]

Escape sequence: \mc

Escape sequence: \m(co

Escape sequence: \m[color]

Register: \n[.m]

Set the stroke color to color.

.gcolor red
The next words
.gcolor
\m[red]are in red\m[]
and these words are in the previous color.

The escape sequence \m[] restores the previous stroke color, as does a gcolor request without an argument.

The name of the current stroke color is available in the read-only string-valued register ‘.m’; it is associated with the environment (see Environments). It interpolates nothing when the stroke color is the default.

\m doesn’t produce an input token in GNU troff (see Gtroff Internals). It therefore can be used in requests like mc (which expects a single character as an argument) to change the color on the fly:

.mc \m[red]x\m[]

Request: .fcolor [color]

Escape sequence: \Mc

Escape sequence: \M(co

Escape sequence: \M[color]

Register: \n[.M]

Set the fill color for objects drawn with \D'…' escape sequences. The escape sequence \M[] restores the previous fill color, as does an fcolor request without an argument.

The name of the current fill color is available in the read-only string-valued register ‘.M’; it is associated with the environment (see Environments). It interpolates nothing when the fill color is the default. \M doesn’t produce an input token in GNU troff.

Create an ellipse with a red interior as follows.

\M[red]\h'0.5i'\D'E 2i 1i'\M[]