(facemenu-unlisted-faces): Add foreground and background color faces.

(facemenu-unlisted-faces): Add foreground and background color faces.
(facemenu-get-face): Delete function.
(facemenu-set-face-from-menu): Don't call facemenu-get-face.
(facemenu-add-new-color): Make second argument mandatory.  Create the
approprate face and return it.  Simplify.
(facemenu-set-foreground, facemenu-set-background): Don't check if
color is defined.  Use return value of facemenu-add-new-color.