[R] transparent colors

[Markus Loecher]

Dear R graphics experts,
Do you know of any way of plotting semi-transparent points in R ?
I face this problem any time I want to e.g. plot thousands of points  
that belong to two or three classes which I color code.
With the default opaque colors, the plotting order matters and  
basically the points I plot last completely dominate the picture. I  
would much rather have the overlaying points mix in color..

Thanks a lot,
Markus