\documentclass[a4paper]{article}

\usepackage{pgfplots}

\usepgfplotslibrary{patchplots}
\pgfplotsset{compat=1.6}

\begin{document}

\begin{tikzpicture}
%\tracingmacros=2 \tracingcommands=2
\begin{axis}
	\addplot3[
		patch,
		patch type=bilinear,
		shader=interp,
		mesh/color input=explicit mathparse,
		domain=0:1,
		samples=5,
		point meta/symbolic={x,y,0},%
		]
	{x*y};
\end{axis}
\end{tikzpicture}

\end{document}

