Similar to how the pick-an-attribute menu for menu colors and
status highlights shows the attribute names using the attribute
so that you can see how it looks (or whether it is supported),
have the pick-a-color menu show the color names in the
corresponding color. Does so by temporarily removing any
user-specified menu colors and setting up another list of such
for matching color names.
Forces the 'menucolors' option On while the pick-a-color menu is
in use, then restores the previous setting along with the user's
menu colorings. Might need some way to avoid setting that for a
configuration where colors don't work.