Re: Colored equations? (particularly compiling to HTML)

[Gwern Branwen <gwern-v26ZT+9V8bxeoWH0uzbU5w@public.gmane.org>]

On Wed, Mar 18, 2020 at 11:27 PM Gwern Branwen <gwern-v26ZT+9V8bxeoWH0uzbU5w@public.gmane.org> wrote:
> In an earlier discussion of Pandoc->Docx (
> https://groups.google.com/d/msgid/pandoc-discuss/aa5ab201-d3a6-44e2-807d-3f92a97f7a8b%40googlegroups.com
> ), John says that the texmath package doesn't support the necessary
> TeX color library, so you can't simply write out color annotations in
> native TeX expressions with $/$$.
> People writing Latex->PDF presumably can just use that color library directly.

So to follow this up more, the weakest link seems to be Texmath.

On the server-side end, the Latex 'xcolor' package is imported by
default by Pandoc, so anyone writing Markdown->PDF can just use colors
directly without even modifying the imports or anything:

https://bookdown.org/yihui/rmarkdown-cookbook/font-color.html

> For PDF, we can use the LaTeX command \textcolor{}{}. This requires the LaTeX package xcolor, which is included in Pandoc’s default LaTeX template.

Which is also confirmed by https://pandoc.org/MANUAL.html#creating-a-pdf

And on the other hand, on the client-side end, Mathjax also supports
color in equations:
https://docs.mathjax.org/en/latest/input/tex/extensions/color.html

> This extension is loaded automatically when the autoload extension is used. ...The color extension defines the \color macro as in the LaTeX color package, along with \colorbox, \fcolorbox, and \definecolor. It declares the standard set of colors (Apricot, Aquamarine, Bittersweet, and so on), and provides the RGB, rgb, and grey-scale color spaces in addition to named colors...in version 3 (and in LaTeX itself), you would do
>
> `{\color{red} x} + {\color{blue} y}`

So we have the situation that if you write Latex directly for Mathjax
in your final HTML, it works fine (example:
https://adereth.github.io/blog/2013/11/29/colorful-equations/ ), and
if you write Latex directly in your Markdown, it works fine by default
(for PDFs), but then it doesn't work at all* if you write Markdown for
HTML?

* I thought initially https://github.com/chdemko/pandoc-latex-color
might work but the README is confusing and it seems to be for the
special-case of colorizing body text, not equations, and for
Markdown->PDF only. There don't seem to be any other relevant filters
for color. So I suppose you would have to go the full-blown 'render
arbitrary LaTeX as SVG/PNG and inline' filter route in order to do
Markdown->HTML colorized equations?

-- 
gwern
https://www.gwern.net

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