Re: Introducing face in comments for various modes

[Christopher Dimech]

> Sent: Tuesday, December 13, 2022 at 3:22 AM
> From: "Yuri Khan" <yuri.v.khan@gmail.com>
> To: "Thibaut Verron" <thibaut.verron@gmail.com>
> Cc: "Heime" <heimeborgia@protonmail.com>, "Stefan Monnier" 
> <monnier@iro.umontreal.ca>, help-gnu-emacs@gnu.org
> Subject: Re: Introducing face in comments for various modes
>
> On Mon, 12 Dec 2022 at 17:53, Thibaut Verron <thibaut.verron@gmail.com> wrote:
> 
> > > If you use "modus-vivendi" for org-mode, the colours are all almost white,
> > > a big problem particularly when you fold the org headings.
> >
> > I don't like dark backgrounds, but it seems perfectly readable to me.
> 
> Heime has a point. The complaint is not about *readability* of
> modus-vivendi’s colors against the background. It is about
> *distinction* between levels of Org headings, i.e. ability to
> distinguish a level 3 heading from a level 4 just by color.
> 
> This is a nontrivial thing to solve, by the way. It’s very easy to
> fall in the trap “WCAG level AAA prescribes a contrast ratio of at
> least 7:1; I’ll make my primary foreground and all my accent
> foreground colors exactly 7:1 against the background so all will be
> readable”. Yes, but this way they are all the same luminance, and by
> that token all very similar in some sense. A color-blind person might
> even not be able to distinguish hues and rely on luminance alone to
> tell colors apart.
> 
> As far as I can tell, WCAG does not give any guidance as to
> distinction between foreground colors, except for “thou shalt not make
> the user rely solely on color”.
 
For modus-themes I suggested a foreground implementation based on a colour
wheel, using a tricolour scheme for fixing adjacent colours.  A technique that
work very well, improving on the original modus-themes colours.

With such metric, one can have about 8 colours, which you can recycle over 
again.