[pstricks] problem with transparency

[xlogo at free.fr]

Hello,

First, thanks for the great pstricks package.

I've tried to define an alpha channel with the example at:

http://tug.org/PSTricks/main.cgi?file=Examples/Colors/colors#transparency

However, when I compile the latex document with latex, dvips and ps2pdf, the
three circles don't have any transparency. the green is under the red that is
under the blue. What's the problem please?

Best
Loïc