https://tex.stackexchange.com/q/547542/35864

leo-ul.tex

\documentclass[a4paper,11pt]{article}
\usepackage[a4paper,includeheadfoot,margin=2.54cm]{geometry} % for margins on a A4paper
\usepackage{xcolor} % for highlighting AND background images-color!!!
\usepackage{luacolor,lua-ul} %for usage of style attributes - background color
\newcommand{\cText}[3][RGB]{%
    \begingroup
    \definecolor{hlcolor}{#1}{#2}\LuaULSetHighLightColor{hlcolor}%
    \highLight{#3}%
    \endgroup
}
\definecolor{RGB2}{RGB}{35, 111, 161}
\definecolor{HTML3}{HTML}{bfedd2}

\begin{document}
Test z% translated tag: span
{\cText[HTML]{7e8c8d}
    {wecks U%
       {\LARGE msetzung von größeren} % [2] <== not working
       {\color{HTML3}{}
        {\LARGE HTML}
           Text
       }-Entities \&<
    }
} 
\end{document}