Twocolumn: Zugriff auf die Spalte, in der ein Label steht ("\columnref")

\documentclass{article}
\usepackage{lipsum} 
\usepackage[left=1cm,right=1cm,top=1cm,bottom=1cm]{geometry}
\usepackage{xcolor}

%% necessary packages
\usepackage[colaction]{multicol}
\usepackage{etoolbox}

\makeatletter
\AtBeginDocument
  {%
    \let\collabel@label\label
    \patchcmd\collabel@label{\@bsphack}{}{}{\harders@labelpatch@error}%
    \patchcmd\collabel@label{\@esphack}{}{}{\harders@labelpatch@error}%
  }
\newcommand\collabel[1]
  {%
    \@bsphack
    \collabel@label{#1}%
    \protected@write\@auxout{}{\string\harders@collabel{#1}}%
    \@esphack
  }
\newcommand\harders@collabel[1]
  {%
    \expandafter\harders@collabel@\expandafter{\harders@cur@col}{#1}%
  }
\newcommand\harders@collabel@[2]
  {%
    \global\@namedef{r@col@#2}{#1}%
  }
\newcommand\colref[1]
  {%
    \@ifundefined{r@col@#1}
      {\@latex@warning{Column reference `#1' on page \thepage\space undefined}}%
      {\csname r@col@#1\endcsname}%
  }
\newcounter{harders@col@count}
\def\harders@patch@last
  {%
    \stepcounter{harders@col@count}%
    \protected@write\@auxout{}%
      {%
        \def\protect\harders@cur@col{\arabic{harders@col@count}}%
      }%
  }
\def\harders@patch@else
  {%
    \ifmc@firstcol
      \setcounter{harders@col@count}{0}%
    \fi
    \harders@patch@last
  }
\def\harders@patch@error
  {%
    \GenericError{}
      {Patching of \string\mc@col@status@write\space failed}
      {%
        Make sure `colaction` was set as an option for `multicol`.%
        \MessageBreak
        Else you're screwed, don't use the code provided here.\MessageBreak%
      }
      {No further help available.}%
  }
\newcommand*\harders@labelpatch@error
  {%
    \GenericError{}{Patching of \string\label\space failed}
      {You shouldn't worry too much, that's not a big issue}
      {No further help available.}%
  }
\pretocmd\mc@lastcol@status@write{\harders@patch@last}{}{\harders@patch@error}
\pretocmd\mc@col@status@write{\harders@patch@else}{}{\harders@patch@error}
\makeatother

\begin{document}
\begin{multicols*}{5}
\lipsum[1]
\lipsum[4]
\textcolor{red}
  {here is the label (\refstepcounter{equation}\theequation\collabel{foo})}
\lipsum[3]
\lipsum[4-7]
\textcolor{red}{here is the reference (\ref{foo}) in column \colref{foo}}
\lipsum[8]
\lipsum[9]
\end{multicols*}
\end{document}