Shaded Venn diagrams

[Scott Lamb <slamb slamb org>]

I'm trying to make a Venn diagram with Dia. I managed to create 
overlapping circles to represent the concepts I want to show. I turned 
off the background as suggested in this email - 
<http://www.mail-archive.com/dia-list lysator liu se/msg03177.html>. 
But it's not very easy to understand. 
<http://www.slamb.org/svn/repos/projects/atoms/doc/descriptors.dia>.

I think it would be a lot clearer if I could have better shading. Is it 
possible in Dia to have the shading of two objects mix in their 
overlapping region? I.e., could I make the Streams color greenish, the 
Pollable color reddish, and have their overlap yellowish? I think that 
would make this a much better diagram.

Thanks,
Scott Lamb