Table Background color with toprule

Question

I want make a table with background color, when I am using \toprule,\midrule and \bottomrule I have a white space after the rule. I want to fill the color of rule below space. MWE is below

\documentclass{book}
\usepackage{amsmath,amsfonts,amssymb}
\usepackage{xcolor}
\usepackage{booktabs}
\usepackage[table]{colortbl}
\usepackage{array}
\abovetopsep=2pt
\makeatletter
\def\toprule{\noalign{\ifnum0=`}\fi
@aboverulesep=\abovetopsep
\global@belowrulesep=4pt%%%I should need 4pt in below of midrule
\global@thisruleclass=@ne
@ifnextchar[{@BTrule}{@BTrule[\heavyrulewidth]}%
}
\def\midrule{\noalign{\ifnum0=`}\fi
@aboverulesep=\abovetopsep
\global@belowrulesep=4pt%%%I should need 4pt in below of midrule
\global@thisruleclass=@ne
@ifnextchar[{@BTrule}{@BTrule[\lightrulewidth]}}
\makeatother
\newcommand{\mc}[2]{\multicolumn{#1}{c}{#2}}
\definecolor{Gray}{gray}{0.85}
\definecolor{LightCyan}{rgb}{0.88,1,1}
\newcolumntype{b}{>{\columncolor{Gray}}c}
\begin{document}
\begin{table}
\begin{tabular}{b | b | b | b | b}
\toprule
\rowcolor{LightCyan}
\mc{1}{}  & \mc{1}{x} & \mc{1}{y} & \mc{1}{w} & \mc{1}{z} \
\rowcolor{LightCyan}
\mc{1}{e}  & \mc{1}{d} & \mc{1}{c} & \mc{1}{b} & \mc{1}{a} \
\cmidrule{1-2}
variable 1 & a & b & c & d \
variable 1 & a & b & c & d \
\midrule
variable 1 & a & b & c & d \
variable 1 & a & b & c & d \
\hline
variable 2 & a & b & c & d \ \bottomrule
\end{tabular}
\end{table}
\end{document}

Answer 1

In order to achieve the effect, you have to do the following

• reset length names that control space above and below rules in booktabs

\setlength{\aboverulesep}{0pt}
\setlength{\belowrulesep}{0pt}

• manually add missing spacing using \rule[]{}{}.

---

EDIT. With tabularray, the code can be much simplified (see the second code)

Note, in this example, I applied booktabs environment instead of regular tblr (both from tabularray). The former keep standard spacing around rows and maintains additional spacing around rules (similarly to booktabs in regular tabular). On the other hand, tblr applies its own layout: rows have slightly larger height as well as rules defined in booktabs do not apply extra spacing.

The MWE without tabularray

\documentclass{book}
\usepackage{amsmath,amsfonts,amssymb}
\usepackage{xcolor}
\usepackage{booktabs}
\usepackage[table]{colortbl}
\usepackage{array}
\newcommand{\mc}[2]{\multicolumn{#1}{c}{#2}}
\definecolor{Gray}{gray}{0.85}
\definecolor{LightCyan}{rgb}{0.88,1,1}
\newcolumntype{B}{>{\columncolor{Gray}}c}   % don't use existing names
\begin{document}
\begin{table}[tbh]
    \begin{tabular}{B | B | B | B | B}
        \specialrule{\heavyrulewidth}{0pt}{0pt}
        \rowcolor{LightCyan}
        \mc{1}{}  & \mc{1}{x} & \mc{1}{y} & \mc{1}{w} & \mc{1}{z} \
        \rowcolor{LightCyan}
        \mc{1}{e}  & \mc{1}{d} & \mc{1}{c} & \mc{1}{b} & \mc{1}{a} \
        \cmidrule{1-2}
        variable 1 & a & b & c & d \
        variable 1 & a & b & c & d \
        \midrule
        variable 1 & a & b & c & d \
        variable 1 & a & b & c & d \
        \hline
        variable 2 & a & b & c & d \ \bottomrule
    \end{tabular}
\end{table}
\begin{table}[tbh]
    \setlength{\aboverulesep}{0pt}
    \setlength{\belowrulesep}{0pt}
    \newcommand\astrut{\rule[8pt]{0pt}{2pt}}
    \newcommand\bstrut{\rule[-5pt]{0pt}{5pt}}
    \begin{tabular}{B *4{|B}}
        \specialrule{\heavyrulewidth}{0pt}{0pt}
        \rowcolor{LightCyan}
        \mc{1}{}   & \mc{1}{x} & \mc{1}{y} & \mc{1}{w} & \mc{1}{z} \
        \rowcolor{LightCyan}
        \mc{1}{e}  & \mc{1}{d} & \mc{1}{c} & \mc{1}{b} & \mc{1}{a\bstrut} \
        \cmidrule{1-2}\astrut
        variable 1 & a & b & c & d \
        variable 1 & a & b & c & d \bstrut \
        \midrule\astrut
        variable 1 & a & b & c & d \
        variable 1 & a & b & c & d \bstrut \
        \hline \astrut
        variable 2 & a & b & c & d \bstrut\ \bottomrule
    \end{tabular}
\end{table}
\end{document}

---

The MWE with tabularray

\documentclass{book}
% \usepackage{amsmath,amsfonts,amssymb}
\usepackage{xcolor}
    \definecolor{Gray}{gray}{0.85}
    \definecolor{LightCyan}{rgb}{0.88,1,1}
\usepackage{tabularray}
    \UseTblrLibrary{booktabs}
\begin{document} 
\begin{table}[tbh]
    \begin{booktabs}{
            colspec = {*5{Q[c]}},
            row{1-2} = {bg=LightCyan},
            row{3-Z} = {bg=Gray},
            hline{3} = {3-5}{Gray},
            rows = {abovesep+=-0pt, belowsep+=-0pt},
        }
        \toprule
           & x & y & w & z \
        e  & d & c & b & a \
        \cmidrule{1-2}
        variable 1 & a & b & c & d \
        variable 1 & a & b & c & d \
        \midrule
        variable 1 & a & b & c & d \
        variable 1 & a & b & c & d \
        \midrule
        variable 2 & a & b & c & d \
        \bottomrule
    \end{booktabs}
\end{table}
\end{document}

Answer 2

With {NiceTabular} of nicematrix.

\documentclass{book}
\usepackage{amsmath,amsfonts,amssymb}
\usepackage{xcolor}
\usepackage{booktabs}
\usepackage{nicematrix}
\begin{document}
\begin{table}
\begin{NiceTabular}{c|c|c|c|c}
\toprule
\Block[fill=[rgb]{0.88,1,1}]{2-}{} % the \Block avoids the vertical rules
& x & y & w & z \
e & d & c & b & a \
\cline{1-2}
\RowStyle[nb-rows=,rowcolor=[gray]{0.85}]{}
variable 1 & a & b & c & d \
variable 1 & a & b & c & d \
\midrule
variable 1 & a & b & c & d \
variable 1 & a & b & c & d \
\hline
variable 2 & a & b & c & d \ \bottomrule
\end{NiceTabular}
\end{table}
\end{document}

You need several compilations (because nicematrix uses PGF/Tikz nodes under the hood).

You won't see thin white lines in the colored panels, whatever PDF viewer you use.