It looks like GIMP currently treats everything as sRGB, regardless of whether it might be tagged or not.

Trivial demonstration:
See http://color.org/version4html.xalter
Download http://color.org/Lower_Left.jpg , which is the lower-left corner of the image
Open that file in GIMP

You'll notice that the rendering is completely wrong, and matches the "The system does not support these ICC profiles" case.

To double-check, I opened the image in geeqie, which renders it correctly.  Both geeqie and GIMP use liblcms to handle color profiles, which suggests that something in GIMP is broken.


Another manifestation of this problem is that "Image->Mode->Assign Color Profile..." has no effect on the appearance of the image.  Thus, the icc-profile parasite is not affecting rendering.  As a corollary, converting an image to sRGB causes it to appear correctly, as the "render as sRGB" assumption becomes true.


From what I've seen of the color management code, the easiest explanation of this behavior is if the icc-profile parasite is not being read when the image is being rendered.  In that case, GIMP will assume by default that the image's color profile is sRGB.


My head commits are:
gegl: ac8fe1d697a8639bffdec8e5ad5d2e832771fbcd
babl: acbb0a9400a8e70d15b3267eafa8451471edb759
gimp: 7b320c7bf66156b6fc1c8b556a42fdaf14a187db
liblcms1: version 1.18.dfsg-1.2+b3

Mikachu is also seeing this with:
gegl: d06d291e (probably d06d291e1992200a204b26bb089ac124ab67ec26)
babl: a210d25 (probably a210d25b28b5d6c59e11dd35f54e5e0739edee95)
gimp: 60242667 (60242667be7038fbeb9e1782f5594d3828c927ee)
liblcms1: version 1.19

owen_ mentioned that (s)he's *not* seeing this:
gegl: 700379f6733c9279592498b4a071c00da99715b2
babl: acbb0a9400a8e70d15b3267eafa8451471edb759
gimp: eb0591f97dca152ec827db083f910b6a9ea16369
liblcms1: some version of 1.18