bug#61188: 30.0.50; color-lighten-name seems not to work

[Eli Zaretskii]

> Cc: 61188@debbugs.gnu.org
> From: Stephen Berman <stephen.berman@gmx.net>
> Date: Mon, 30 Jan 2023 23:58:26 +0100
> 
> On Mon, 30 Jan 2023 21:48:20 +0000 "Mark Bestley" <gnu@bestley.co.uk> wrote:
> 
> > Look at the results of
> >
> > (require 'color)
> > (message "reduce by 100 = %s" (color-lighten-name "Black" 100))
> > (message "reduce by 0 = %s" (color-lighten-name "Black" 0))
> >
> > In emacs 28.2 they give "#ffffffffffff" and 0 as expected.
> > In emacs 30.0.50 they give 0 and 0
> 
> This difference is due to this commit:
> 
> commit 656c2dd66e77a5fbeb99d358017e8327401fae05
> Author:     Lars Ingebrigtsen <larsi@gnus.org>
> Commit:     Lars Ingebrigtsen <larsi@gnus.org>
> CommitDate: Tue Mar 22 15:28:02 2022 +0100
> 
>     Fix color-lighten-hsl logic
> 
>     * lisp/color.el (color-lighten-hsl): Lighten by percentage,
>     instead of just adding the specified number to the luminance
>     element (bug#54514).
> 
> The patch below restores the Emacs 28 result for the above examples
> while keeping the desired result for the example in bug#54514, but I
> have no idea if it yields undesirable results in other cases.

If all the tests in color-tests.el pass after the change, please
install on the release branch.

Thanks.