I'd like to colorize the empty cell in row #2 and also the merged rows. How can I do this?
\documentclass{article}
\begin{document}
\begin{center}
\begin{tabular}{ |c| c| c |c |c |c|}
\hline
chapter & \multicolumn{5}{|c|}{rules in sub-chapters} \\
\hline
& first & second & third& fourth & total \\
\hline
first & 75 & 73 & 93 & 110 & 351 \\
\hline
second & 72 & 38 & 73 & 85 & 268 \\
\hline
total & \multicolumn{4}{|c|}{} & 3981 \\
\hline
\end{tabular}
\end{center}
\end{document}


diagbox. – TeXnician Feb 11 '17 at 18:19