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(elisp)Text Terminal Colors

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Text Terminal Colors
====================

   Emacs can display color on text-only terminals, starting with version
21.  These terminals support only a small number of colors, and the
computer uses small integers to select colors on the terminal.  This
means that the computer cannot reliably tell what the selected color
looks like; instead, you have to inform your application which small
integers correspond to which colors.  However, Emacs does know the
standard set of colors and will try to use them automatically.

   Several of these functions use or return "rgb values".  An rgb value
is a list of three integers, which give the amount of red, the amount
of green, and the amount of blue.  Each integer ranges in principle
from 0 to 65535, but in practice the largest value used is 65280.

   These functions accept a display (either a frame or the name of a
terminal) as an optional argument.  We hope in the future to make Emacs
support more than one text-only terminal at one time; then this argument
will specify which terminal to operate on (the default being the
selected frame's terminal; Note: Input Focus).  At present, though,
the DISPLAY argument has no effect.

 - Function: tty-color-define name number &optional rgb display
     This function associates the color name NAME with color number
     NUMBER on the terminal.

     The optional argument RGB, if specified, is an rgb value; it says
     what the color actually looks like.  If you do not specify RGB,
     then this color cannot be used by `tty-color-approximate' to
     approximate other colors, because Emacs does not know what it looks
     like.

 - Function: tty-color-clear &optional display
     This function clears the table of defined colors for a text-only
     terminal.

 - Function: tty-color-alist &optional display
     This function returns an alist recording the known colors
     supported by a text-only terminal.

     Each element has the form `(NAME NUMBER . RGB)' or `(NAME
     NUMBER)'.  Here, NAME is the color name, NUMBER is the number used
     to specify it to the terminal.  If present, RGB is an rgb value
     that says what the color actually looks like.

 - Function: tty-color-approximate rgb &optional display
     This function finds the closest color, among the known colors
     supported for DISPLAY, to that described by the rgb value RGB.

 - Function: tty-color-translate color &optional display
     This function finds the closest color to COLOR among the known
     colors supported for DISPLAY.  If the name COLOR is not defined,
     the value is `nil'.

     COLOR can be an X-style `"#XXXYYYZZZ"' specification instead of an
     actual name.  The format `"RGB:XX/YY/ZZ"' is also supported.