Unintended Tabular Colouring MWE

\documentclass{article}
\usepackage{etoolbox}
\usepackage[table]{xcolor}
\usepackage{booktabs} % or ctable

\colorlet{text}{black}
\colorlet{page}{white}
\colorlet{tableheadcolor}{orange!30!page}

% The use of \showrowcolors and \hiderowcolors is an idea from Ulrike
% Fischer's answer here: <https://tex.stackexchange.com/a/494954/73317>
\renewcommand{\toprule}{%
    \showrowcolors
    \arrayrulecolor{text}\specialrule{\heavyrulewidth}{\abovetopsep}{0pt}%
    \arrayrulecolor{tableheadcolor}\specialrule{\belowrulesep}{0pt}{0pt}%
    \arrayrulecolor{text}%
    \rowcolor{tableheadcolor}%
}

\apptocmd\midrule{\hiderowcolors}{}{\FAILED}

\makeatletter

\let\@BTrule@ORI=\@BTrule
\let\my@BTrule=\@BTrule

% Modified version of \@BTrule that doesn't do \vskip\@aboverulesep, for use
% when the corresponding vertical space should be coloured.
\patchcmd{\my@BTrule}{%
    \ifnum\@lastruleclass=\z@\vskip\@aboverulesep\else
  }{%
    \ifnum\@lastruleclass=\z@\else
  }{}{\FAILED}

\let\@arraycrORI=\@arraycr

% The “master counter” hackery is explained in the TeXbook appendix D (Dirty
% Tricks), pp. 385-386. It is also mentioned in the array.sty implementation
% notes concerning \@arraycr.
\renewcommand*{\@arraycr}{%
  % Increase the master counter. This is needed to prevent TeX from
  % prematurely finishing the alignment entry in case \\ was followed by '&'
  % (when the \futurelet from \@ifnextchar causes TeX to read a '&', this
  % finishes the entry unless the master counter has a different value than it
  % had when the entry was started).
  \relax\iffalse{\fi\ifnum 0=`}\fi
  % Each of the two branches takes care of decreasing the master counter.
  \@ifnextchar\midrule
    {\@firstoftwo{\my@endtablehead}}% gobble the following \midrule
    {\my@closebrace@and@arraycrORI}%
}

\newcommand*{\my@endtablehead}{%
 \ifnum 0=`{}\fi % the second brace decreases the master counter
 \@arraycrORI[\aboverulesep]% this colours the additional space with the
                            % current row color
 \noalign{\global\let\@BTrule\my@BTrule}% temporarily modify \@BTrule
 \midrule
 \noalign{\global\let\@BTrule\@BTrule@ORI}% restore it
}

\newcommand*{\my@closebrace@and@arraycrORI}{%
  \ifnum 0=`{}\fi % the second brace decreases the master counter
  \@arraycrORI
}

\makeatother

\rowcolors{1}{tableheadcolor}{tableheadcolor}

\begin{document}
\pagecolor{blue!10}

\begin{tabular}{l}
    a \\
    b \\
    c
\end{tabular}

\bigskip

\begin{tabular}{l}
    \midrule
\end{tabular}

\bigskip

\begin{tabular}{l}
    a \\
    b \\
    c
\end{tabular}

\end{document}