Table cell color overlaps cell border

Question

As the graphic and MWE below show, some of colored my table cells are obscured the cell colors. I'd appreciate help fixing this.

\documentclass[english]{article}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\usepackage[table]{xcolor}

\makeatletter
\providecommand{\tabularnewline}{\\}
\makeatother

\usepackage{babel}
\begin{document}
\begin{tabular}{c|c|c|c|cc|}
\multicolumn{1}{c}{} & \multicolumn{1}{c}{A} & \multicolumn{1}{c}{B} & \multicolumn{1}{c}{C} & D & \multicolumn{1}{c}{E}\tabularnewline
\cline{2-6} 
a & \cellcolor{blue!25} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} &  & \cellcolor{red!25} \tabularnewline
\cline{2-3} 
b &  &  & \multicolumn{1}{c}{} &  & \tabularnewline
\cline{2-4} 
c &  &  &  &  & \tabularnewline
\cline{2-5} 
d &  &  &  & \multicolumn{1}{c|}{} & \tabularnewline
\cline{2-6} 
e &  & \cellcolor{green!25} &  & \multicolumn{1}{c|}{} & \tabularnewline
\cline{2-6} 
\end{tabular}
\end{document}

Answer 1

You can use hhline here which simply adds vertical space and doesn’t get over-drawn by \cellcolor.

Code

\documentclass{standalone}
\usepackage[table]{xcolor}
\usepackage{hhline}
\begin{document}
\begin{tabular}{c|c|c|c|cc|}
    \multicolumn{1}{c}{} & \multicolumn{1}{c}{A} & \multicolumn{1}{c}{B} & \multicolumn{1}{c}{C} &           D           & \multicolumn{1}{c}{E} \tabularnewline \hhline{~|*{5}{-}}
             a           &  \cellcolor{blue!25}  & \multicolumn{1}{c}{}  & \multicolumn{1}{c}{}  &                       &  \cellcolor{red!25}   \tabularnewline \cline{2-3}
             b           &                       &                       & \multicolumn{1}{c}{}  &                       &  \tabularnewline \cline{2-4}
             c           &                       &                       &                       &                       &  \tabularnewline \cline{2-5}
             d           &                       &                       &                       & \multicolumn{1}{c|}{} &  \tabularnewline \hhline{~|*5-}
             e           &                       & \cellcolor{green!25}  &                       & \multicolumn{1}{c|}{} &  \tabularnewline \hhline{~|*5-}
\end{tabular}
\end{document}

Output

Answer 2

The environment {NiceTabular} of the package nicematrix has tools design to address that kind of problem.

\documentclass[margin=1cm]{standalone}
\usepackage{nicematrix}
\usepackage{xcolor}

\begin{document}
\begin{NiceTabular}{ccccc}[first-row,first-col,hvlines]
\CodeBefore
  \cellcolor{blue!25}{1-1}
  \cellcolor{red!25}{1-5}
  \cellcolor{green!25}{5-2}
\Body
  & A & B & C & D & E \\
a &   & \Block{1-*}{} & \Block{2-1}{} & \Block{3-1}{} & \Block{4-1}{} \\
b &   &   & \Block{1-*}{} \\
c &   &   &   & \Block{1-*}{} \\
d &   &   &   &   & \Block{1-*}{} \\
e \\
\end{NiceTabular}
\end{document}

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