On saving gamma
When saving an image as PNG in GIMP you are facing the choice of checking option save gamma or not. When you check it — according to official GIMP documentation — the gamma value of your display environment is embedded into the PNG file. I was resizing the Gentoo logo, file gblend.png. Checking save gamma on export results in the left (correct) image, leaving it unchecked in the right: too far towards purple.
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If you use Firefox or Thunderbird these two images look different. To my recent surprise they look identical in all of GWenview 4.6.2, gthumb 2.12.3 and Thunar 1.2.1. Interestingly, now that I have seen the difference I notice that the logo shown on gentoo-wiki.com does not have correct gamma. See for yourself. I have contacted its operator about it, let's see what happens. I don't really have time to inspect this issue much further. If you do that would be awesome. Please send patches to upstream for me. Thank you!
EDIT : Mike has updated the logo on gentoo-wiki.com by now.