I would like to underline and color only the first letre which is "I" for Information and C for Communication, also color the underlining but this line color all the texte with red !!
\color{red}{\underline{\color{blue} I}}nformation and \underline{C}ommunication
You can create a command with xparse \Underline that can also take an optional color value that defaults to a color of your choice, in the example blue.
\documentclass{article}
\usepackage{xcolor}
\begin{document}
\NewDocumentCommand\Underline{O{blue}m}{\underline{\textcolor{#1}{#2}}}
\Underline[red]Information and \Underline Communication
\end{document}
\textcolor{red}{\underline{\color{blue} I}}nformation and \underline{C}ommunication? Please don't post code fragments. Always add a short, but compilable test file instead, which allows us to reproduce the problem. It should include a class, the necessary packages and adocumentenvironment. – samcarter_is_at_topanswers.xyz Jan 19 '24 at 12:40