Table coloring with multirow and multicolumn

Question

I'm trying to have get a background color at my tables consisting of both multirows and multicolums. Without any color, the table works fine. But what I want to color expands over variable amounts of rows. I've tried to color four rows with the same color, with one cell stretching over four rows and one cell stretching over two rows.

But if I do that the second coloring, applies the color on top of the multirow text.

As you can see, the second line of rowcolor removes the upper part of 'Grade' from cell 1 and third row color removed the lower part of 'Grade' and lower part of Thickness. Any solution ideas?

my tex:

\begin{table}[ht]
\begin{tabular}{|c|c|lll|}
\hline
\rowcolor{blue!20} 
\multirow{4}{*}{Grades}&Yield&\multicolumn{3}{c|}{Impact bending test}\\
\rowcolor{blue!20}
                      &Strength&\multirow{2}{*}{Thickness}&Test& Impact\\
\rowcolor{blue!20}
                             &$\mathbf{R_e[N/mm^2]}$&                                &{\bf temperature}     & {\bf work}\\
\rowcolor{blue!20}
                             &\bf{transv.min.}      &\bf{ transv.}                   &$\mathbf{[\grader]}$  & {\bf [J]} \\\hline
\multirow{ 1}{*}{{\bf DH36}}   &     & {\bf 5.5 – 7.0} & {\bf         -40} & {\bf       24} \\

\hline
\end{tabular}
\end{table}

Answer 1

Based on guessing about your preamble and meaning of used commands:

\documentclass{article}
\usepackage{siunitx}
\usepackage{makecell,multirow}
\usepackage[table]{xcolor}

\begin{document}
    \begin{table}[htb]
\sisetup{detect-weight=true}
\renewcommand\arraystretch{1.3}
\begin{tabular}{|*{2}{>{\bfseries}c|}
                 *{3}{>{\bfseries}c}|}
    \hline
\rowcolor{blue!20}
                &   &   \multicolumn{3}{c|}{\textbf{Impact bending test}}    \\
\rowcolor{blue!20}
\multirow{-2}*{Grades}  
        &   \multirow{-3}*[-1ex]{\makecell{Yield\\  Strength\\ 
                                            {$\mathbf{R_e[\si{N\per\milli\meter^2}]}$} \\transv. min.}}
                    &   \makecell{Thickness\\  transv.}    
                        &   \makecell{Test\\ temperature\\ \si{\celsius}}
                            &   \makecell{Impact\\ work\\ \si{J} }          \\
    \hline
DH36   &       & 5.5 – 7.0 & -40   & 24    \\
    \hline
\end{tabular}
    \end{table}
\end{document}

Edit: macro makecell have options b for bottom position, t for top position, l for left aligned cell content and r for right aligned. Use of it without options the cell content is vertically and horizontally centered.

If in above MWE replace the second row of table with

\multirow{-3}*{Grades}
        &   \multirow{-3}*[3pt]{\makecell{Yield\\  Strength\\
                                            {$\mathbf{R_e[\si{N\per\milli\meter^2}]}$} \\transv. min.}}
                    &   \makecell[b]{Thickness\\  transv.}
                        &   \makecell[b]{Test\\ temperature\\ \si{\celsius}}
                            &   \makecell[b]{Impact\\ work\\ \si{J} }          \\

than the table is as follows:

Answer 2

Here is how you can do that table with {NiceTabular} of nicematrix. You won't see thin white lines, wathever PDF viewer you use.

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

\begin{document}

\begin{table}[htb]
\sisetup{detect-weight=true}
\renewcommand\arraystretch{1.3}
\begin{NiceTabular}{|c|c|ccc|}[cell-space-top-limit=3pt]
\Hline
\RowStyle[nb-rows=2,rowcolor=blue!20]{\bfseries}
\Block{2-1}{Grades} 
   & \Block{2-1}{Yield\\ Strength\\ $\mathbf{R_e[\unit{N\per\milli\meter^2}]}$ \\transv. min.}  
     & \Block{1-3}{Impact bending test}  \\
   &   
     & \Block{}{Thickness\\  transv.}    
       & \Block{}{Test\\ temperature\\ \unit{\celsius}}
          & \Block{}{Impact\\ work\\ \unit{J}}   \\
\Hline
DH36  &  & $5.5$ -- $7.0$ & $-40$ & $24$    \\
\Hline
\end{NiceTabular}
\end{table}

\end{document}

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