\documentclass{ppex}
\nonstopmode
\usepackage {pstcol,pst-3d}
\pagestyle{empty}
\setlength\textwidth{183.0pt}
\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage {pstcol,pst-3d}
\begin{pspicture}(-5,-3)(4,3)
 \psset{unit=.3cm}
 \psset{viewpoint=-1 -1 1}
 \ThreeDput[normal=0 0 1]{\psgrid(-3,-3)(6,6)}
 \ThreeDput[normal=-1 0 0](0,4,0){
   \psframe*[linecolor=yellow](4,4)}
\end{pspicture}
\end{document}