table header problems with \multicolumn

Question

I have been trying to produce some aesthetically appealing tables for my MSc thesis. This link has helped me a lot: Professional-looking tables with alternating row colors?

A challenge, however, remains. I really do not know how to use the information presented by the aforementioned link to produce a table with a multiple-line heading. I will try to make things a tad easier to understand with an example:

This is the code I have:

\begin{table}[htp]
\begin{center}
\renewcommand{\arraystretch}{1.5}
\begin{tabular}{l r r}
\topline
\headcol statement & \multicolumn{2}{c}{mean rates}  \\
\headcol  & system A & system B \\
\midline
      1. statement 1 & \textbf{4.2} & 4.1\\
\rowcol 2. statement 2 & \textbf{3.8} & 3.7 \\
      3. statement 3 & \textbf{4.2} & 4.0 \\
\rowcol 4. statement 4 & \textbf{4.3 }& 4.2\\
\bottomlinec
\end{tabular}
\end{center}
\caption[First table]{First table}
\label{tab:statements_group_1}
\end{table}

I used the following definitions (from the previous link)

\documentclass{article}
\usepackage{booktabs}% http://ctan.org/pkg/booktabs
\usepackage{colortbl}% http://ctan.org/pkg/colortbl
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\usepackage{xcolor}% http://ctan.org/pkg/xcolor
\usepackage{graphicx}% http://ctan.org/pkg/graphicx
\colorlet{tableheadcolor}{gray!25} % Table header colour = 25% gray
\newcommand{\headcol}{\rowcolor{tableheadcolor}} %
\colorlet{tablerowcolor}{gray!10} % Table row separator colour = 10% gray
\newcommand{\rowcol}{\rowcolor{tablerowcolor}} %
% Command \topline consists of a (slightly modified) \toprule followed a \heavyrule rule of colour tableheadcolor (hence, 2 separate rules)
\newcommand{\topline}{\arrayrulecolor{black}\specialrule{0.1em}{\abovetopsep}{0pt}%
\arrayrulecolor{tableheadcolor}\specialrule{\belowrulesep}{0pt}{0pt}%
\arrayrulecolor{black}}
% Command \midline consists of 3 rules (top colour tableheadcolor, middle colour black, bottom colour white)
\newcommand{\midline}{\arrayrulecolor{tableheadcolor}  \specialrule{\aboverulesep}{0pt}{0pt}%
\arrayrulecolor{black}\specialrule{\lightrulewidth}{0pt}{0pt}%
\arrayrulecolor{white}\specialrule{\belowrulesep}{0pt}{0pt}%
\arrayrulecolor{black}}
% Command \rowmidlinecw consists of 3 rules (top colour tablerowcolor, middle colour black, bottom colour white)
\newcommand{\rowmidlinecw}{\arrayrulecolor{tablerowcolor}  \specialrule{\aboverulesep}{0pt}{0pt}%
\arrayrulecolor{black}\specialrule{\lightrulewidth}{0pt}{0pt}%
\arrayrulecolor{white}\specialrule{\belowrulesep}{0pt}{0pt}%
\arrayrulecolor{black}}
% Command \rowmidlinewc consists of 3 rules (top colour white, middle colour black, bottom colour tablerowcolor)
\newcommand{\rowmidlinewc}{\arrayrulecolor{white}\specialrule{\aboverulesep}{0pt}{0pt}%
\arrayrulecolor{black}\specialrule{\lightrulewidth}{0pt}{0pt}%
\arrayrulecolor{tablerowcolor}\specialrule{\belowrulesep}{0pt}{0pt}%
\arrayrulecolor{black}}
% Command \rowmidlinew consists of 1 white rule \newcommand{\rowmidlinew}   {\arrayrulecolor{white}\specialrule{\aboverulesep}{0pt}{0pt}%
\arrayrulecolor{black}}
% Command \rowmidlinec consists of 1 tablerowcolor rule
\newcommand{\rowmidlinec}{\arrayrulecolor{tablerowcolor}  \specialrule{\aboverulesep}{0pt}{0pt}%
\arrayrulecolor{black}}
% Command \bottomline consists of 2 rules (top colour
 \newcommand{\bottomline}{\arrayrulecolor{white}\specialrule{\aboverulesep}{0pt}{0pt}%
 \arrayrulecolor{black}\specialrule{\heavyrulewidth}{0pt}{\belowbottomsep}}%
 \newcommand{\bottomlinec}{\arrayrulecolor{tablerowcolor}  \specialrule{\aboverulesep}{0pt}{0pt}%
\arrayrulecolor{black}\specialrule{\heavyrulewidth}{0pt}{\belowbottomsep}}%

I was wondering if you could help me find out why part of the header (mean rates) is not coloured in dark grey.

Answer 1

This was too long to be a comment, so I used an answer.

You accidentally commented out part of the code given in the answer to the question you linked to and left some spurious code with unbalanced braces. The problem is in the line starting with

% Command \rowmidlinew consists of 1 white rule \newcommand{\rowmidlinew}...

Only the first part

% Command \rowmidlinew consists of 1 white rule

has to be commented; not the \newcommand... part.

Once this is corrected, as in my code below, your example code will run without errors and will produce the desired output:

\documentclass{article}
\usepackage{booktabs}% http://ctan.org/pkg/booktabs
\usepackage{colortbl}% http://ctan.org/pkg/colortbl
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\usepackage{xcolor}% http://ctan.org/pkg/xcolor
\usepackage{graphicx}% http://ctan.org/pkg/graphicx
\colorlet{tableheadcolor}{gray!25} % Table header colour = 25% gray
\newcommand{\headcol}{\rowcolor{tableheadcolor}} %
\colorlet{tablerowcolor}{gray!10} % Table row separator colour = 10% gray
\newcommand{\rowcol}{\rowcolor{tablerowcolor}} %
% Command \topline consists of a (slightly modified) \toprule followed a \heavyrule rule of colour tableheadcolor (hence, 2 separate rules)
\newcommand{\topline}{\arrayrulecolor{black}\specialrule{0.1em}{\abovetopsep}{0pt}%
\arrayrulecolor{tableheadcolor}\specialrule{\belowrulesep}{0pt}{0pt}%
\arrayrulecolor{black}}
% Command \midline consists of 3 rules (top colour tableheadcolor, middle colour black, bottom colour white)
\newcommand{\midline}{\arrayrulecolor{tableheadcolor}  \specialrule{\aboverulesep}{0pt}{0pt}%
\arrayrulecolor{black}\specialrule{\lightrulewidth}{0pt}{0pt}%
\arrayrulecolor{white}\specialrule{\belowrulesep}{0pt}{0pt}%
\arrayrulecolor{black}}
% Command \rowmidlinecw consists of 3 rules (top colour tablerowcolor, middle colour black, bottom colour white)
\newcommand{\rowmidlinecw}{\arrayrulecolor{tablerowcolor}  \specialrule{\aboverulesep}{0pt}{0pt}%
\arrayrulecolor{black}\specialrule{\lightrulewidth}{0pt}{0pt}%
\arrayrulecolor{white}\specialrule{\belowrulesep}{0pt}{0pt}%
\arrayrulecolor{black}}
% Command \rowmidlinewc consists of 3 rules (top colour white, middle colour black, bottom colour tablerowcolor)
\newcommand{\rowmidlinewc}{\arrayrulecolor{white}\specialrule{\aboverulesep}{0pt}{0pt}%
\arrayrulecolor{black}\specialrule{\lightrulewidth}{0pt}{0pt}%
\arrayrulecolor{tablerowcolor}\specialrule{\belowrulesep}{0pt}{0pt}%
\arrayrulecolor{black}}
% Command \rowmidlinew consists of 1 white rule 
\newcommand{\rowmidlinew}{\arrayrulecolor{white}\specialrule{\aboverulesep}{0pt}{0pt}%
\arrayrulecolor{black}}
% Command \rowmidlinec consists of 1 tablerowcolor rule
\newcommand{\rowmidlinec}{\arrayrulecolor{tablerowcolor}  \specialrule{\aboverulesep}{0pt}{0pt}%
\arrayrulecolor{black}}
% Command \bottomline consists of 2 rules (top colour
 \newcommand{\bottomline}{\arrayrulecolor{white}\specialrule{\aboverulesep}{0pt}{0pt}%
 \arrayrulecolor{black}\specialrule{\heavyrulewidth}{0pt}{\belowbottomsep}}%
 \newcommand{\bottomlinec}{\arrayrulecolor{tablerowcolor}  \specialrule{\aboverulesep}{0pt}{0pt}%
\arrayrulecolor{black}\specialrule{\heavyrulewidth}{0pt}{\belowbottomsep}}%

\begin{document}

\begin{table}[htp]
\begin{center}
\renewcommand{\arraystretch}{1.5}
\begin{tabular}{l r r}
\topline
\headcol statement & \multicolumn{2}{c}{mean rates}  \\
\headcol  & system A & system B \\
\midline
      1. statement 1 & \textbf{4.2} & 4.1\\
\rowcol 2. statement 2 & \textbf{3.8} & 3.7 \\
      3. statement 3 & \textbf{4.2} & 4.0 \\
\rowcol 4. statement 4 & \textbf{4.3 }& 4.2\\
\bottomlinec
\end{tabular}
\end{center}
\caption[First table]{First table}
\label{tab:statements_group_1}
\end{table}
\end{document}