elisp: Color Names
28.21 Color Names
=================
A color name is text (usually in a string) that specifies a color.
Symbolic names such as ‘black’, ‘white’, ‘red’, etc., are allowed; use
‘M-x list-colors-display’ to see a list of defined names. You can also
specify colors numerically in forms such as ‘#RGB’ and ‘RGB:R/G/B’,
where R specifies the red level, G specifies the green level, and B
specifies the blue level. You can use either one, two, three, or four
hex digits for R; then you must use the same number of hex digits for
all G and B as well, making either 3, 6, 9 or 12 hex digits in all.
(See the documentation of the X Window System for more details about
numerical RGB specification of colors.)
These functions provide a way to determine which color names are
valid, and what they look like. In some cases, the value depends on the
“selected frame”, as described below; see 
Input Focus, for the
meaning of the term “selected frame”.
To read user input of color names with completion, use ‘read-color’
(read-color High-Level Completion.).
-- Function: color-defined-p color &optional frame
This function reports whether a color name is meaningful. It
returns ‘t’ if so; otherwise, ‘nil’. The argument FRAME says which
frame’s display to ask about; if FRAME is omitted or ‘nil’, the
selected frame is used.
Note that this does not tell you whether the display you are using
really supports that color. When using X, you can ask for any
defined color on any kind of display, and you will get some
result—typically, the closest it can do. To determine whether a
frame can really display a certain color, use ‘color-supported-p’
(see below).
This function used to be called ‘x-color-defined-p’, and that name
is still supported as an alias.
-- Function: defined-colors &optional frame
This function returns a list of the color names that are defined
and supported on frame FRAME (default, the selected frame). If
FRAME does not support colors, the value is ‘nil’.
This function used to be called ‘x-defined-colors’, and that name
is still supported as an alias.
-- Function: color-supported-p color &optional frame background-p
This returns ‘t’ if FRAME can really display the color COLOR (or at
least something close to it). If FRAME is omitted or ‘nil’, the
question applies to the selected frame.
Some terminals support a different set of colors for foreground and
background. If BACKGROUND-P is non-‘nil’, that means you are
asking whether COLOR can be used as a background; otherwise you are
asking whether it can be used as a foreground.
The argument COLOR must be a valid color name.
-- Function: color-gray-p color &optional frame
This returns ‘t’ if COLOR is a shade of gray, as defined on FRAME’s
display. If FRAME is omitted or ‘nil’, the question applies to the
selected frame. If COLOR is not a valid color name, this function
returns ‘nil’.
-- Function: color-values color &optional frame
This function returns a value that describes what COLOR should
ideally look like on FRAME. If COLOR is defined, the 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 some displays may not use the full range.
This three-element list is called the “rgb values” of the color.
If COLOR is not defined, the value is ‘nil’.
(color-values "black")
⇒ (0 0 0)
(color-values "white")
⇒ (65280 65280 65280)
(color-values "red")
⇒ (65280 0 0)
(color-values "pink")
⇒ (65280 49152 51968)
(color-values "hungry")
⇒ nil
The color values are returned for FRAME’s display. If FRAME is
omitted or ‘nil’, the information is returned for the selected
frame’s display. If the frame cannot display colors, the value is
‘nil’.
This function used to be called ‘x-color-values’, and that name is
still supported as an alias.
Info Catalog
elisp: Drag and Drop
elisp: Frames
elisp: Text Terminal Colors