30.12.5 Colors in Formatted Text
You can specify foreground and background colors for portions of the
text. There is a menu for specifying the foreground color and a menu
for specifying the background color. Each color menu lists all the
colors that you have used in Enriched mode in the current Emacs session.
If you specify a color with a prefix argument—or, in Transient
Mark mode, if the region is not active—then it applies to any
immediately following self-inserting input. See Transient Mark.
Otherwise, the command applies to the region.
Each color menu contains one additional item: ‘Other’. You can use
this item to specify a color that is not listed in the menu; it reads
the color name with the minibuffer. To display a list of available colors
and their names, use the ‘Display Colors’ menu item in the Text
Properties menu (see Editing Format Info).
Any color that you specify in this way, or that is mentioned in a
formatted text file that you read in, is added to the corresponding
color menu for the duration of the Emacs session.
There are no key bindings for specifying colors, but you can do so
with the extended commands M-x facemenu-set-foreground and
M-x facemenu-set-background. Both of these commands read the name
of the color with the minibuffer.