Picasa, Gimp, and Shotwell all use dcraw to convert from raw.
I had off-colors because the version of dcraw included in my distribution did not yet properly support my camera (Canon G11).
I compiled dcraw myself, which is dead-easy. I put the binary in my path which solved the problem except for Picasa.
Picasa uses dcraw but brings its own version and I don't know if it is possible to replace it. Luckily for me the current version of picasa (3.8) had a recent version of dcraw.
See http://www.webupd8.org/2010/04/how-to-install-picasa-36-in-ubuntu.html on how to install Picasa 3.8 in Linux.
I made a quick test with dcraw 9.04 and dcraw 9.05, see below:
Result from dcraw 9.04
Result from dcraw 9.05 (2010/11/11)
If you need help compiling an setting up dcraw write a comment.
I can tell you what I did to get it working but I think it is off-topic here.