Are beamer, hhline, and [table]{xcolor} incompatible?

Question

The following example works as expected:

\documentclass{article}
\usepackage[table]{xcolor}
\usepackage{makecell, multirow}
    \renewcommand\theadfont{\normalsize\bfseries\color{white}}
    \renewcommand{\theadgape}{}
\usepackage{hhline}

\begin{document}
\centering
    \setlength\arrayrulewidth{2pt}
    \arrayrulecolor{yellow}
    \def\clinecolor{\hhline{>{\arrayrulecolor{yellow}}--%
                            >{\arrayrulecolor{gray}}-}}
    \setlength\extrarowheight{2pt}
\begin{tabular}{ c | c | c }%
    \rowcolor{gray}
\multicolumn{2}{c|}{\thead{AAA -- BBBB}}    &                                   \\
    \clinecolor
    \rowcolor{gray}
\color{white} AAA   &   \color{white} BBB   &   \multirow{-2}{*}{\thead{CCC}}   \\
    \hhline{>{\arrayrulecolor{yellow}}-|-|-}
    \rowcolor{gray!25}
aaa                 &   bbb                 &   ccc                             \\
    \hline
    \rowcolor{gray!25}
ddd             &   eee                 &   fff
    \end{tabular}
\end{document}

But the following not:

\documentclass[xcolor=table]{beamer}
\usepackage{makecell, multirow}
    \renewcommand\theadfont{\normalsize\bfseries\color{white}}
    \renewcommand{\theadgape}{}
\usepackage{hhline}

\begin{document}
\begin{frame}
\frametitle{test}
\centering
    \setlength\arrayrulewidth{2pt}
    \arrayrulecolor{yellow}
    \def\clinecolor{\hhline{>{\arrayrulecolor{yellow}}--%
                            >{\arrayrulecolor{gray}}-}}
    \setlength\extrarowheight{2pt}
\begin{tabular}{ c | c | c }%
    \rowcolor{gray}
\multicolumn{2}{c|}{\thead{AAA -- BBBB}}    &                                   \\
    \clinecolor
    \rowcolor{gray}
\color{white} AAA   &   \color{white} BBB   &   \multirow{-2}{*}{\thead{CCC}}   \\
    \hhline{>{\arrayrulecolor{yellow}}-|-|-}
    \rowcolor{gray!25}
aaa                 &   bbb                 &   ccc                             \\
    \hline
    \rowcolor{gray!25}
ddd             &   eee                 &   fff                             \\
    \hhline{|-|-|-|}
    \end{tabular}
\end{frame}
\end{document}

Why are the in beamer rules so strangely misplaced? Is there some workaround?

Answer 1

as samcarter commented

\documentclass[xcolor=table]{beamer}
\usepackage{makecell, multirow}
    \renewcommand\theadfont{\normalsize\bfseries\color{white}}
    \renewcommand{\theadgape}{}
\usepackage{hhline}
\makeatletter
\let\zz\reset@color
\def\reset@color{\kern\z@\zz}
\makeatother

\begin{document}
\begin{frame}
\frametitle{test}
\centering
    \setlength\arrayrulewidth{2pt}
    \arrayrulecolor{yellow}
    \def\clinecolor{\hhline{>{\arrayrulecolor{yellow}}--%
                            >{\arrayrulecolor{gray}}-}}
    \setlength\extrarowheight{2pt}
\begin{tabular}{ c | c | c }%
    \rowcolor{gray}
\multicolumn{2}{c|}{\thead{AAA -- BBBB}}    &                                   \\
    \clinecolor
    \rowcolor{gray}
\color{white} AAA   &   \color{white} BBB   &   \multirow{-2}{*}{\thead{CCC}}   \\
    \hhline{>{\arrayrulecolor{yellow}}-|-|-}
    \rowcolor{gray!25}
aaa                 &   bbb                 &   ccc                             \\
    \hline
    \rowcolor{gray!25}
ddd             &   eee                 &   fff                             \\
    \hhline{|-|-|-|}
    \end{tabular}
\end{frame}
\end{document}

Answer 2

Use booktabs instead – more precisely set \above/belowrulesep to 0pt and use \midrule:

\documentclass[xcolor=table]{beamer}
\usepackage{makecell, multirow}
\usepackage{booktabs}
\renewcommand\theadfont{\normalsize\bfseries\color{white}}
\renewcommand{\theadgape}{}

\begin{document}

\begin{frame}
  \frametitle{test}
  \centering
  \setlength\arrayrulewidth{2pt}
  \setlength\extrarowheight{2pt}
  \setlength\belowrulesep{0pt}\setlength\aboverulesep{0pt}
  \setlength\lightrulewidth{2pt}
  \arrayrulecolor{yellow}
  \begin{tabular}{ c | c | c }%
    \rowcolor{gray}
    \multicolumn{2}{c|}{\thead{AAA -- BBBB}} & \\
    \midrule
    \rowcolor{gray}
    \color{white} AAA & \color{white} BBB & \multirow{-2}{*}{\thead{CCC}} \\
    \midrule
    \rowcolor{gray!25}
    aaa & bbb & ccc \\
    \midrule
    \rowcolor{gray!25}
    ddd & eee & fff \\
  \end{tabular}
\end{frame}

\end{document} 

Answer 3

A variant with the tabularray package:

\documentclass{beamer}
\usepackage{tabularray}
\begin{document}
\begin{frame}
\centering
\begin{tblr}{
  colspec={ccc},
  row{1-2}={bg=gray,fg=white},
  row{1}={font=\bfseries},
  row{3-Z}={bg=lightgray},
  hline{2-Y}={yellow,wd=2pt},
  vline{2-Y}={yellow,wd=2pt},
}
\SetCell[c=2]{} AAA - BBBB & & \SetCell[r=2]{} CCC \
AAA & BBB  & \
aaa & bbb & ccc \
ddd & eee & fff
\end{tblr}
\end{frame}
\end{document}

Answer 4

With {NiceTabular} of nicematrix, you have a key hvlines-except-borders to draw all the rules, excepted on the borders and in the blocks (created by \Block).

\documentclass{article}
\usepackage{xcolor}
\usepackage{nicematrix}
\begin{document}
\begin{center}
\arrayrulecolor{yellow}
\setlength{\arrayrulewidth}{2pt}
\setlength{\extrarowheight}{2pt}
\setlength{\tabcolsep}{10pt}
\begin{NiceTabular}{ccc}[hvlines-except-borders]
\RowStyle[nb-rows=2,color=white,rowcolor=gray]{}
\RowStyle[bold]{}
\Block{1-2}{AAA - BBBB} & & \Block{2-1}{CCC} \
AAA & BBB \
\RowStyle[nb-rows=2,rowcolor=gray!25]{}
aaa & bbb & ccc \
ddd & eee & fff
\end{NiceTabular}
\arrayrulecolor{black}
\end{center}
\end{document}

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

The result may seem disappointing. The vertical rules protrude below the array by a length equal to \arrayrulewidth by design... It's useful to have perfect joins with vertical rules in the most common situations...

However, with nicematrix (version ≥ 6.12), it's possible to draw a white rule at the end with \Hline[color=white].

\documentclass{article}
\usepackage{xcolor}
\usepackage{nicematrix,tikz}
\begin{document}
\begin{center}
\arrayrulecolor{yellow}
\setlength{\arrayrulewidth}{2pt}
\setlength{\extrarowheight}{2pt}
\setlength{\tabcolsep}{10pt}
\begin{NiceTabular}{ccc}[hvlines-except-borders]
\RowStyle[nb-rows=2,color=white,rowcolor=gray]{}
\RowStyle[bold]{}
\Block{1-2}{AAA - BBBB} & & \Block{2-1}{CCC} \
AAA & BBB \
\RowStyle[nb-rows=2,rowcolor=gray!25]{}
aaa & bbb & ccc \
ddd & eee & fff
\Hline[color=white] 
\end{NiceTabular}
\arrayrulecolor{black}
\end{center}
\end{document}

But there is another way. It's possible to define a new type of rule with its letter (I) and its command \MyLine and use it in the preamble and between the rows.

\documentclass{article}
\usepackage{xcolor}
\usepackage{nicematrix,tikz}
\NiceMatrixOptions
  {
    custom-line = 
     {
       letter = I , 
       command = MyLine ,
       total-width = 2pt , 
       tikz = { line width = 2pt , yellow }
     }
  }
\begin{document}
\begin{center}
\setlength{\arrayrulewidth}{0pt}
\begin{NiceTabular}{cIcIc}[columns-width=15mm,cell-space-limits=3pt]
\RowStyle[nb-rows=2,color=white,rowcolor=gray]{}
\RowStyle[bold]{}
\Block{1-2}{AAA - BBBB} & & \Block{2-1}{CCC} \
\MyLine
AAA & BBB \
\MyLine
\RowStyle[nb-rows=2,rowcolor=gray!25]{}
aaa & bbb & ccc \
\MyLine
ddd & eee & fff
\end{NiceTabular}
\arrayrulecolor{black}
\end{center}
\end{document}

Now, the vertical rules protrude below the array by a value of \arrayrulewidth but the value of \arrayrulewidth is zero. So, the output is perfect.