I think he's talking about ICC color profiles, support for which is usually provided via ColorSync on Macs. IE and OmniWeb both support this.
Gecko used to support ICC profiles, but people complained that it made images look "too dark" on Macs (never mind that this was how the images were originally intended to be viewed), so they removed that feature. It was removed before Chimera really got started, so it has never been in that browser.
Safari's an oddball. Either PNG's or CSS colors support ICC profiles; I don't know which. But whichever one does, the other one doesn't, and this can cause problems.
I don't know about iCab or Opera.