I’ve been struggling with PNG colour matching for a while. It’s fine on my Linux boxes, with a standard sRGB colour profile, but on Macs and Win/IE with an ICCP in place, the colours never match up with the CSS colours. This is always frustrating, as PNGs are so nice for proper alpha transparency.
I just found this handy snippet out there in the ether, to get rid of the gamma and colour profile info from PNGs.
pngcrush -d outputdir -rem gAMA -rem cHRM -rem iCCP *.png
pngcrush also optimizes the file and reduces the size, which is nice. Handy little tool.