\cellcolor removes \hline

Question

I have a table where I am filling some of the cells with a gray color. It works fine. The problems is however, that the horizontal lines of the table becomes gray too. How can I solve this so that the lines stays as Black lines and the cell color is gray?

Image of my problem:

A complete code example can be found online here or in this code:

\documentclass{article}
\usepackage{slashbox,pict2e}
\usepackage{color, colortbl}
\usepackage{amssymb}

\definecolor{Gray}{gray}{0.9}

\begin{document}

\begin{table}
\centering
\begin{tabular}{|l|c|c|c|}
    \hline\backslashbox{Enhed}{Interface} & ED    & DDG   & \textit{Server} \\
    \hline  ED      & \checkmark        & \checkmark        & {\cellcolor{Gray}} \\
    \hline DDG     & \checkmark        & {\cellcolor{Gray}}  & \checkmark \\
    \hline \textit{Server}  & {\cellcolor{Gray}}  & \checkmark        & {\cellcolor{Gray}}\\\hline
\end{tabular}
\caption{Oversigt over interfaces mellem enhederne.}
\label{tab:interfacesMellemEnheder}
\end{table}
\end{document}

Answer 1

As you can read in the comments there never was a problem with the tex code. The only problem was the pdf viewer. When zooming in the lines gets visible again. This will not be a problem when printing the page.

Answer 2

The environment {NiceTabular} of nicematrix (≥ 4.0 2020-05-08) gives a solution to that problem.

With colortbl, a \hline is drawn and, if there is a colored cell in the following row, the colored rectangle is drawn after the horizontal rule. Even if the position of the rule and of the colored rectangle are mathematically exact, almost all PDF viewers give priority to the colored rectangle (explicitly drawn after in the PDF): they consider that, at a low zoom level, the rules drawn before are only detail less important (that's why it's difficult to say that this is a 'issue' of the viewer).

With nicematrix, this problem is solved because all the rules are drawn after the colored rectangles (rows, columns, cells, etc.).

Moreover, nicematrix provides a command \diagbox and a key hvlines to draw all the rules.

\documentclass{article}
\usepackage{xcolor}
\usepackage{amssymb}
\usepackage{nicematrix}
\begin{document}
\begin{table}
\centering
\begin{NiceTabular}{wl{2.2cm}ccc}[hvlines]
\CodeBefore
  \cellcolor{lightgray}{2-4,3-3,4-2,4-4}
\Body
\rule[-3mm]{0pt}{9mm}
\diagbox{Enhed}{Interface} & ED    & DDG   & \textit{Server}  \
  ED                       & \checkmark    & \checkmark     &  \
 DDG                       & \checkmark    &                & \checkmark \
 \textit{Server}           &               & \checkmark     & \
\end{NiceTabular}
\caption{Oversigt over interfaces mellem enhederne.}
\label{tab:interfacesMellemEnheder}
\end{table}
\end{document}

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

Answer 3

Sorry, this is too long for a comment. As requested by FireFly3000, an example with booktabs with only a few rules:

In this type of table diagbox have no utility, so you can put "Interface" in a multicolumn in a previous row, and left only "Enhed" in the cell, or if you prefer this label vertically centered, use the multirow package:

\documentclass{article}
\usepackage{colortbl, booktabs}
\usepackage{multirow}
\usepackage{amssymb}
\definecolor{Gray}{gray}{0.9}
\begin{document}
\begin{table}
\centering
\begin{tabular}{lccc}
\toprule
\multirow{2}{*}{Enhed} & \multicolumn{3}{c}{Interface} \\
\cmidrule{2-4}
            & ED                &  DDG             & \textit{Server} \\
\midrule
ED               & \checkmark        & \checkmark       & \cellcolor{Gray} \\
DDG              & \checkmark        & \cellcolor{Gray} & \checkmark       \\
\textit{Server}  & \cellcolor{Gray}  & \checkmark       & \cellcolor{Gray} \\
\bottomrule
\end{tabular}

\caption{Oversigt over interfaces mellem enhederne.}
\label{tab:interfacesMellemEnheder}
\end{table}
\end{document}

Answer 4

A simple solution is just to increase the table linewidth. The PDF viewer will then no longer have the issue.

\setlength\arrayrulewidth{1pt} %Increasing linewidth \begin{table} (...) \end{table} \setlength\arrayrulewidth{0.4pt} %Back to default