bug#51556: 29.0.50; Poor contrast of Customize SVG icons with dark backgrounds

[Kévin Le Gouguec]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Kévin Le Gouguec <kevin.legouguec@gmail.com>
>> Date: Mon, 01 Nov 2021 18:56:13 +0100
>> 
>> On darker themes (e.g. modus-vivendi), the Customize SVG icons
>> (etc/images/right.svg and etc/images/down.svg) are not very visible, due
>> to the poor contrast between their fill color (#2e3436) and dark
>> backgrounds[1].
>
> That's for the themes to resolve, isn't it?  They could supply their
> own icons, because only they know which colors will go well with the
> theme's colors.

That's sort of what I suggest?  In the rest of my message, I propose
allowing widgets to apply faces to their icons (:on-glyph and
:off-glyph), so that themes can customize these faces.  This should work
for all SVG images that do not define a fill color.

Or is there a way for themes to define sets of icons?  "(elisp) Custom
Themes" describes custom-theme-set-variables and custom-theme-set-faces,
but I couldn't find anything related to icons.

Or are you suggesting adding the ability for themes to include sets of
icons?  That seems a bit heavy-handed to me; I don't think a lot of
theme authors will want to bother with SVG editing.  For the purposes of
this bug, merely letting themes customize the icon color (through faces)
ought to be enough?

I'm not sure which path forward you prefer (if any).  Sorry for being
slow.