@nethryk
I used Picasa for a few years but basically
just for the straightening tool.
But I always noticed a slight loss of sharpness after
the stamps were straightened.
Also I hated when after opening Picasa it went through every
pic on my hard drive, over and over again.
Now I use Fast Stone Image Viewer for straightening.
It's a bit slower to use but there is no blurring
like with Picasa.
Here is your Jean Racine Scott 629 from the "Drama and Theatre" thread on the left beside mine on the right.
Colour wise, neither looks like the actual stamp though yours
might be slightly more true.
France Scott 629 1948
Designer : André Spitz
Engraver:
Achille Ouvré 
Scott calls the colour
sepia, Yvert Tellier claims it's
brun violacé (Purplish brown) and Michel says it is
brownish black.
What I see on my scan is mostly black, maybe a smidgen of purple.
I see graphis uses the Epson Perfection V5000 Photo and I believe
you have also stated in the past that you use the same
Epson model.
I have the older version the Epson Perfection 4490 Photo,
so perhaps the newer V5000 is more colour sensitive.