+@cindex color names
+@cindex specify color
+@cindex numerical RGB color specification
+ A color name is text (usually in a string) that specifies a color.
+Symbolic names such as @samp{black}, @samp{white}, @samp{red}, etc.,
+are allowed; use @kbd{M-x list-colors-display} to see a list of
+defined names. You can also specify colors numerically in forms such
+as @samp{#@var{rgb}} and @samp{RGB:@var{r}/@var{g}/@var{b}}, where
+@var{r} specifies the red level, @var{g} specifies the green level,
+and @var{b} specifies the blue level. You can use either one, two,
+three, or four hex digits for @var{r}; then you must use the same
+number of hex digits for all @var{g} and @var{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.)
+