RE: list-colors-display: display all color names

[Drew Adams]

    With #RRGGBB values printed in the *Colors* buffer it would be possible
    to find closer color names even without a function, simply with a regexp
    isearch like M-C-s #f.[fe].e.  It will not find the closest color name,
    but it is good enough to help to find all closer colors.

    Even better would be if the *Colors* buffer was sorted by RGB values.
    I don't suggest to do that by default, but different sorting order would
    be useful, e.g. by color name, by color intensity.  The latter is good
    for finding a darker or brighter color than a given color, but it is not
    so obvious since there are too many variants of projecting a color value
    from 3-D color space into a 1-D color list.  Perhaps the most useful is
    sorting by hue into a rainbow, and inside every hue sorting by
    value*saturation.

Great idea. There are usually so many colors in `list-colors-display' that
it is hard to find a "good" ordering - what is good for one user at one time
is different from what it is otherwise.

Being able to sort the colors in different ways would be a definite
improvement.
In terms of a default order, I do think that RGB order would be generally
more useful than color name. The current order is ad hoc, BTW - colors are
currently not sorted by name (the order is implementation-dependent, and is
essentially whatever `xw-defined-colors' returns, which is `w32-color-map'
or `x-colors').

    >>> gray         grey               bebebe
    >>> light gray   light grey, LightGray, LightGrey    d3d3d3
    >> First, if we do that, I'd suggest to use #BE12BE34BE56, i.e. prefix
    >> with # and use 4 digits per color.
    > I agree on the `#'.

    I omitted the `#' to save more space.  But OK, one character is not
    too much to remind the users about the proper format.

The # is important for 1) recognition of what this is about and 2)
copy+pasting to Lisp code or to commands that ask for a color.