\usepackage {pstcol,pst-grad}
\begin{pspicture}(0,0)(3,2)\showgrid
\psframe[framearc=0.25,
  fillstyle=gradient,
  gradangle=30,
  gradbegin=yellow,
  gradend=red]
  (0.5,0.5)(2.5,1.5)
\end{pspicture}