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 (see read-color).
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.
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.
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.
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.
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")
⇒ (65535 65535 65535)
(color-values "red")
⇒ (65535 0 0)
(color-values "pink")
⇒ (65535 49344 52171)
(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.
This function does the same as color-values, but it returns
color values as floating-point numbers between 0.0 and 1.0 inclusive.
This function returns non-nil if the color described by its RGB
triplet rgb is more readable against white background than
against dark background. The argument rgb should be a list of
the form (r g b), with each component a
floating-point number in the range 0.0 to 1.0 inclusive. You can use
color-name-to-rgb to convert a color’s name to such a list.