I have worked only in tikz, I want to make an image of 600 px by 300 px so that the edge of the fractal image is a little white blurred and the background of the box has the same color as the attached image.
\documentclass{standalone}
\usepackage{pst-fractal}
\begin{document}
\begin{pspicture}(-20,-6)(4,6)
\psframe*[linecolor=cyan](-4,-4)(4,4)
\psSier[unit=0.25,n=4,fillstyle=solid,fillcolor=yellow,linecolor=blue]
\end{pspicture}
\end{document}

