Span column in a multicols environment

Here's a generalized version of Tom Bombadil's \multicolinterrupt macro: The current value of \col@number is saved before ending the multicols environment, and after typesetting the "interruption" text a new multicols environment with the same number of columns as the last one is started.

\documentclass[parskip]{scrartcl}
\usepackage[margin=15mm]{geometry}
\usepackage{lipsum}
\usepackage{multicol}
\usepackage{xcolor}

\newcounter{tempcolnum}

\makeatletter
\newcommand{\multicolinterrupt}[1]{% Stuff to span both rows
\setcounter{tempcolnum}{\col@number}
\end{multicols}
#1%
\begin{multicols}{\value{tempcolnum}}
}
\makeatother

\begin{document}

\begin{multicols}{3}
\lipsum[1-2]
\multicolinterrupt{\textcolor{blue}{\lipsum[3-4]}}
\lipsum[5-6]
\end{multicols}

\end{document}

Probably like this?

\documentclass[parskip]{scrartcl}
\usepackage[margin=15mm]{geometry}
\usepackage{lipsum}
\usepackage{multicol}
\usepackage{xcolor}

\newcommand{\multicolinterrupt}[1]{% Stuff to span both rows
\end{multicols}
#1
\begin{multicols}{2}
}

\begin{document}

\begin{multicols}{2}
\lipsum[1-2]
\multicolinterrupt{\textcolor{blue}{\lipsum[3-4]}}
\lipsum[5-6]
\end{multicols}

\end{document}