\documentclass{article}
\reversemarginpar
\usepackage{calc,xcolor}
\newlength\fullwidth
\setlength\fullwidth{\textwidth+2\marginparsep}
\newcommand\mpar[2][]{\marginpar{\parbox{\marginparwidth}{\raggedleft #1}%
  \rlap{\hspace*{\fullwidth}{\parbox{\marginparwidth}{#2}}}}}

\def\x{foo bar baz und auch mal lorum ipsum und so weiter}
\begin{document}

Im Anfang \mpar[\color{red}one ten hundred]{\color{blue}two three 
four five six seven} war 
das Wort. \x\x\x\x\mpar[\color{red}left]{\color{blue}right} \x\x\x\x

\end{document}