after spending some more time about my problem on how to emulate
transparency to create nice eps figures with shaded areas,
I found this web page:
So I decided to implement the algorithm and it seems that the approach
works (see attached pdf).
Of course if there are many layers of transparent colors, it would be
very hard to get the exact colors, but so far it's the best approach
that I've found.
The code can be downloaded from here:
show_mimic_alpha.pdf (77.8 KB)
show_mimic_alpha_red_background.pdf (46.3 KB)