'mathml'-option does not color equations

[yalguzaq]

Consider the following TeX:

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[english]{babel}
\usepackage{amsmath,amsthm,amsfonts,amssymb}
\usepackage{hyperref}
\usepackage{xcolor}

\begin{document}
$$\text { minimize } {{\color{blue} x_6} + {\color{blue} x_7} + {\color{blue} x_8}}$$
A basic feasible solution to the auxiliary problem is obtained by letting $({\color{blue} x_6},{\color{blue} x_7},{\color{blue} x_8}) := \mathbf{b} = (2,2,1)$.
\end{document}

I have two issues here:

• Running make4ht markup.tex colors centered equations ($$) but not inline ones ($)
• Running make4ht markup.tex 'mathml,mathjax' does not color anything.

[michal-h21]

This issue is quite complicated to solve, because you can quite easily run into XML tag mismatch with switch commands such as \color. It is better to use \textcolor, which has limited scope. Anyway, you can try this configuration file:

\Preamble{xhtml}

\makeatletter
\catcode`\:=11
\let\current:tag\relax
\def\color:tag{\ifmmode mstyle\else span\fi}
\def\:color:after{\HCode{</\color:tag>}\let\current:tag\relax}
\def\:tmp#1{\get:xcolorcss{#1}\:tmpcolor\def\current:tag{\HCode{<\color:tag}\HCode{ style="color:\:tmpcolor" >}}\current:tag\aftergroup\:color:after\o:color:{#1}}
\HLet\color\:tmp
%\Configure{HtmlPar}{\ifx\current:tag\relax\else\color:after\fi\EndP\HCode{<p>}\current:tag}{\EndP\HCode{<p>}}{\HCode{</p>}}{\HCode{</p>}}
\catcode`\:=12
\makeatother
\begin{document}
\EndPreamble

It fails with more complicated examples, where you use \color outside groups, but it seems to work for your test file.

[yalguzaq]

Thank you. The conclusion is that \textcolor should be used instead.