bug#46396: 27.1.90; Ediff's non-focused diff section, background too light in --reverse

[Juri Linkov <juri@jurta.org>]

tags 46396 fixed
close 46396 28.0.50
thanks

>> Do you see more problems with the following patch?
>
> Juri, this is a definite improvement, thank you. Committing it as it is
> seems reasonable since it makes unreadable text readable again.

Thanks for confirming, now committed to master for Emacs 28.

> I applied this patch and played around with applying various light and
> dark themes.
>
> Some comments:
>
> In the "tango-dark" theme:
>
>  a) the non-current diff backgrounds are quite close to the theme's dark
>     background color, so they are not very noticeable.
>  b) the current diff (such as `ediff-current-diff-B`) is also quite close
>     to the theme's background color.
>
> In the "tango-light" theme:
>
>  c) `ediff-current-diff-A' is quite dark (a darker blue/purple), and the
>     foreground color is hard to read over it. This is a little odd,
>     because `ediff-current-diff-B' is a fairly bright yellow background.
>
> I saw similar issues in the various other standard themes (loading up
> the mater branch with src/emacs -Q).
>
> The issues I see with ediff-current-* faces are arguably a tangent to
> this bug. Perhaps those faces could use :distant-foreground as well, for
> similar reasons?

I'm not sure if it's possible to find such default colors that would
work well for all standard themes.  But there is no need to use
:distant-foreground in themes, because the authors of themes can find
the right combination of the default/ediff colors and adjust their themes
accordingly.

> As for the background colors possibly being quite similar to the theme's
> background, I'm not sure what to do about that.

Implementing something like :distant-background is less important than
:distant-foreground, because :distant-foreground is important to
make the text readable, while :distant-background would only help
making the background color differ from the default background color.