IE can’t do anything right. If you save some graphical elements to PNG, and try to put them on an area with CSS-defined color, there will be a difference even if you used the same color in the PNG — IE renders PNGs darker than it should. The reason for this is misinterpretation of gAMA frame saved in PNGs that makes it possible to better color-match pictures. The fix is to remove this frame, and doing it on Ubuntu is as easy as:

aptitude install pngcrush
cd your-graphics-directory
mkdir fixed
find . -type f -exec pngcrush -d fixed -rem cHRM -rem gAMA -rem iCCP -rem sRGB {} \;


Now you have a „fixed” directory where you have PNGs that will work properly in IE (and are a bit smaller which is a nice side effect). If you’re sure they’re ok, just do

mv fixed/* ./
rmdir fixed


That’s all.