\documentclass[a4paper,10pt]{article}
\usepackage[dvipsnames]{pstricks}
\usepackage{pst-xkey}

\makeatletter
\define@key[psset]{}{stain}{\def\psk@stain{#1}}
\define@key[psset]{}{step}{\def\psk@step{#1}}
\psset{stain=20,step=0.25}% 
%
\def\psCStain{\pst@object{psCStain}}
\def\psCStain@i(#1)#2{%
  \leavevmode
  \pst@killglue
  \begingroup
    \use@par
    \pscircle*(#1){#2}
    \init@pscode%
    \pst@getcoor{#1}\pst@tempa%
    \pssetlength\pst@dimc{#2}%
    \def\pst@linetype{4}%
    \addto@pscode{%    
    rrand srand
    /getRandInt { rand 2147483647 div \psk@stain\space mul } def
    \pst@tempa\space translate 
    /radius \pst@number\pst@dimc \psk@dimen CLW mul sub def
    newpath
    0 radius moveto
    0 \psk@step\space 360 {
      /angle exch def
      radius getRandInt add dup angle cos mul exch angle sin mul
      lineto
    } for
    closepath fill
  }%
  \pst@stroke
  \use@pscode
  \endgroup
  \ignorespaces%
}
\makeatother
\pagestyle{empty}
\parindent=0pt
\begin{document}

\begin{pspicture}(7,2)
  \psCStain[linecolor=red](3.5,1){0.5}
  \psCStain(1,1){0.25}
  \psCStain[linecolor=Goldenrod,step=1](6,1){0.25}
\end{pspicture}

\end{document}
