I try to make a graph with various molecules and their modifications. The differences I want to highlight in red as seen in the picture. Pseudouridine has not only an additional NH but also the double bond shifts. So I would like to just color the inner bond of the double bond. I found this similar question but it does not really my problem.
Has anyone an idea how I can just color one line of a double bond in chemfig?
MWE:
\documentclass{article}
\usepackage{graphicx}
\usepackage{subcaption}
\usepackage{chemfig}
\usepackage{lipsum}
\usepackage{amsmath}
\begin{document}
\begin{figure*}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Molecules
\definesubmol{PU}{*6(=N(-R)-(=O)-NH-(=O)-{\color{red}H}|{\color{red}N}-[,,2])}
\definesubmol{Ubase}{*6(-N(-R)-(=O)-NH-(=O)-=)}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{subfigure}{.2\textwidth}
\chemfig[atom style={scale=0.6}]{!{PU}}
\caption{Pseudouridine ($\Psi$)}\label{fig:Label1}
\end{subfigure}
\hspace*{\fill}
\begin{subfigure}{.2\textwidth}
\chemfig[atom style={scale=0.6}]{!{Ubase}}
\caption{Uridine}\label{fig:Label2}
\end{subfigure}
\hspace*{\fill}
\begin{subfigure}{.2\textwidth}
\caption{}\label{fig:Label3}
\end{subfigure}
\caption{\lipsum[1]}
\end{figure*}
\end{document}