# “! Misplaced \omit” error in multicolumn and BlackCell

I ran into a problem with “! Misplaced \omit” error. I have searched quite hard to find the relevant problem but only find mine is similar with bigbadpiano's question in which A.Ellett generated a nice table with WME.

However, my personal desire is to put one multicolumn as black background and white text, for instance:

This is an failed example since the whole first row should be black. I also get an error in Log File:" ! Misplaced \omit. \multispan ->\omit \@multispan l.10 ...multicolumn{8}{|c|}{\BlackCell{Dataset A}} \\hline I expect to see \omit only after tab marks or the \cr of an alignment. Proceed, and I'll ignore this case."

If this question is duplicate, I am really sorry but I couldn't find the correct answer to my specific problem. In this case, please inform me the exact answer and I will delete this question later. Any help is appreciated.

\documentclass{article}
\pagestyle{empty}
\usepackage[table]{xcolor}
\newcommand\BlackCell[1]{%
\multicolumn{1}{c}{\cellcolor{black}\textcolor{white}{#1}}
}
\begin{document}
\begin{table}[h]
\begin{tabular}{|c|c|c|c|c|c|c|c|}\hline
\multicolumn{8}{|c|}{\BlackCell{Dataset A}} \\\hline
L (m)  & T (s) & T$^2$ (s$^2$) & L$^{1/2}$ (m$^{1/2}$) & $\Delta$T$^2$ (s$^2$) & $\Delta$T (s) & Fitted T$^2$ (s$^2$) & Fitted T (s) \\ \hline
0.2 & 0.626 & 0.392         & 0.447                 & 0.006                 & 0.005         & 0.394                & 0.662 \\
0.3 & 0.889 & 0.790         & 0.548                 & 0.009                 & 0.005         & 0.797                & 0.889 \\
0.4 & 1.105 & 1.221         & 0.632                 & 0.011                 & 0.005         & 1.201                & 1.081 \\
0.5 & 1.261 & 1.590         & 0.707                 & 0.013                 & 0.005         & 1.604                & 1.250 \\
0.6 & 1.420 & 2.016         & 0.775                 & 0.014                 & 0.005         & 2.008                & 1.403 \\
0.7 & 1.555 & 2.418         & 0.837                 & 0.016                 & 0.005         & 2.411                & 1.543 \\
0.8 & 1.679 & 2.819         & 0.894                 & 0.017                 & 0.005         & 2.814                & 1.674 \\
0.9 & 1.798 & 3.233         & 0.949                 & 0.018                 & 0.005         & 3.218                & 1.797 \\
1.0 & 1.901 & 3.614         & 1.000                 & 0.019                 & 0.005         & 3.621                & 1.913 \\
1.1 & 2.000 & 4.000         & 1.049                 & 0.020                 & 0.005         & 4.025                & 2.023 \\\hline
\end{tabular}
\end{table}

\end{document}


You have a \multicolumn inside a \multicolumn which is not allowed (and you had a missing % at end of line). Use
\newcommand\BlackCell[1]{%