How do I get rid of the small lines between cells in a table?

Question

I'm trying to make a table with the first column and row as colored, but the rest of the cells in white. Though it works almost as expected, there's a thin white line between some cells that should be merged I'd love to get help removing them.

Here's the code I have so far:

\documentclass[10pt]{iopart}
\usepackage[table]{xcolor}
\usepackage{multirow}
\usepackage{hhline}
\begin{document}
\begin{table*}
    \begin{tabular}{p{3cm}p{5.25cm}p{5.25cm}}
        \rowcolor{black}
      &\multicolumn{1}{c}{\textbf{\color{white}Title A}} & \multicolumn{1}{c}
      {\textbf{\color{white}Title B}} \\  
         
        \cellcolor{black}\textbf{\color{white}Foo A }
            &   X
            &   Y \\ \hhline{~--}   
        
        \cellcolor{black} & X & Y\\
        \cellcolor{black}& X& Y\\
        \multirow{-3}{*}{\cellcolor{black}\color{white}Foo B}& X& Y\\ \hhline{~--} 

        \cellcolor{black}\textbf{\color{white}Foo C} 
            &   X 
            &   Y\\
        \cellcolor{black}
         &  &   Y \\
        \cellcolor{black}
         &  &   Y \\
    \end{tabular}
    \caption{Caption.}
\end{table*}
\end{document}

It looks like this:

Foo A (Row 2) needs no changing.

Foo C (Rows 6-8) I want to get rid of the white spacing connecting the three rows.

Foo B (Rows 3-5) was my attempt at using a solution I found in this similar question I thought might help by using multirows. Apart from not removing the white line between the cells, it also centers the "Foo B" text vertically, which I don't want.

Ideally, I would like the result to look like this (but with Foo B at the top of its rows):

Thanks!

Answer 1

Package tabularray makes better tables with clean code:

\documentclass[10pt]{article}

\usepackage{xcolor}
\usepackage{tabularray}

\begin{document}

\begin{table*}
  \begin{tblr}{
    colspec = {p{3cm}p{5.25cm}p{5.25cm}},
    row{1} = {bg=gray2,fg=white,c},
    column{1} = {bg=gray2,fg=white,font=\bfseries},
  }   
                           & Title A & Title B \\          
                     Foo A & X       & Y       \\\hline
    \SetCell[r=3]{h} Foo B & X       & Y       \\ 
                           & X       & Y       \\
                           & X       & Y       \\\hline
    \SetCell[r=3]{h} Foo C & X       & Y       \\
                           & X       & Y       \\
                           & X       & Y       \\\hline
  \end{tblr}
  \caption{Caption}
\end{table*}

\end{document}

Inside \SetCell command, r=3 is for mulitrow, and h is for vertical alignment.

Answer 2

Here is a code with the classical package colortbl (loaded by the key table of the package xcolor) which gives a good output.

\documentclass{article}
\usepackage[table]{xcolor}

\begin{document}

\arrayrulecolor{orange}

\begin{table*}

\sffamily

\begin{tabular}{>{\columncolor{black}\color{white}}w{l}{3cm}w{l}{5.25cm}w{l}{5.25cm}}
    \rowcolor{black}
          & \multicolumn{1}{c}{\color{white}Title A} & \multicolumn{1}{c}{\color{white}Title B} \\
    Foo A & X & Y \\ \cline{2-3}
    Foo B & X & Y \\
          & X & Y \\
          & X & Y \\ \cline{2-3}
    Foo C & X & Y \\
          &   & Y \\
          &   & Y \\
\end{tabular}
\caption{Caption.}

\end{table*}

\end{document}

However, there are some thin white lines in the black panels (it depends of the PDF viewer: with PDF.js, used for instance by Firefox, they are usually present).

The package nicematrix has tools to address that problem.

Form the previous code, I will now:

• load nicematrix (and unload colortbl);
• replace {tabular} by {NiceTabular};
• add the key color-inside (alias: colortbl-like) to say that there are instructions of color in the array itself (and not in so-called \CodeBefore provided by nicematrix).

\documentclass{article}
\usepackage{xcolor}
\usepackage{nicematrix}

\begin{document}

\arrayrulecolor{orange}

\begin{table*}

\sffamily

\begin{NiceTabular}{>{\columncolor{black}\color{white}}w{l}{3cm}w{l}{5.25cm}w{l}{5.25cm}}[color-inside]
    \rowcolor{black}
          & \multicolumn{1}{c}{\color{white}Title A} & \multicolumn{1}{c}{\color{white}Title B} \\
    Foo A & X & Y \\ \cline{2-3}
    Foo B & X & Y \\
          & X & Y \\
          & X & Y \\ \cline{2-3}
    Foo C & X & Y \\
          &   & Y \\
          &   & Y \\
\end{NiceTabular}
\caption{Caption.}

\end{table*}

\end{document}

Here is the output (once again copied from Firefox).