Here is a possible solution based on the following packages:
Notice that two compilation runs are necessary to successfully color the margins.
Code:
\documentclass{article}
\usepackage{tikzpagenodes}
\usetikzlibrary{calc}
\usepackage{ifthen}
\usepackage[contents={},opacity=1,scale=1.485]{background}
\AddEverypageHook{%
\ifthenelse{\isodd{\thepage}}%
{\backgroundsetup{angle=0,position={0.9\textwidth,-
.7\textheight},%
contents={\tikz[remember picture,overlay]{ %
\coordinate (x) at (current page marginpar area.south east|-current page.south east);
\draw[draw=none,fill=magenta!20]([xshift=-\textwidth]x)rectangle(current page.north west);}}}}%
{\backgroundsetup{angle=0,position={0.9\textwidth,-
.7\textheight},%
contents={\tikz[remember picture,overlay]{ %
\coordinate (x) at (current page marginpar area.south east|-current page.south east);
\draw[draw=none,fill=orange!20](x)rectangle(current page.north east);}}}}%
\BgMaterial}
\usepackage{lipsum} % dummy text
\begin{document}
\lipsum[1-30]
\end{document}
Result (just the first two pages are displayed):