Here's an example image:
https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-ash4/422086_520757554626335_187862497_n.jpg

When I open it in Iceweasel with the default settings, it renders as the
left half of this picture shows:

http://imageshack.us/a/img266/5517/dhn6.png

So the T-shirt looks dark blue, almost violet. In realit, and in any
other browser, including Firefox on Windows, this T-shirt looks rather
light blue-ish, as the right half of the picture shows. This issue is
most noticeable with Facebook, as they force pictures to so-called
‘sRGB IEC61966-2-1 black scaled’, so each and every picture from
Facebook looks horribly wrong.