'mathml'-option does not recognize \color command

[iabarus]

trafficstars

LaTeX:

\documentclass{article}
\usepackage{xcolor}
\begin{document}
$$\color{blue}{y_1}$$
$$\textcolor{blue}{y_1}$$
\end{document}

Compilation command: make4ht markup.tex 'mathml,mathjax'

Correct output:

Erroneous output:

Problem summary: \textcolor and \color have practically the same syntax but the latter is not processed.