I have a jpeg with embedded color profile that I exported from darktable. That picture looks the same and as intended (i.e. rather dark; with darktable as the reference) in krita, firefox, gimp and pqiv (gdk-pixbuf) but looks washed out and horrible in gwenview, qiv, eog. I tried all color management related settings in gwenview (advanced settings) but that did not seem to change anything.
I run kde plasma 6.4.4 in an x11 session. The color profile I set via the plasma settings is sRGB. When I remove the embedded color profile from the jpeg, the picture looks much darker than intended but uniform across all named applications.
What could be going wrong?
With color profile embedded:
No color profile embedded
I have the same issue here, Plasma Wayland 6.7.1 and Gwenview 26.04.2. I am using a custom ICC profile in the display settings.
The image I am looking at has the Display P3 profile embedded. It looks consistent across GIMP, Firefox, and Okular, but oversaturated in Gwenview. Tweaking the color management settings also does not make it look like it does in the other applications.
It may not be the same issue. Color management on Wayland works completely differently compared to X11.
In any case, looks like for some reason Gwenview itself converts all images with an embedded color profile to sRGB, regardless of any compositor color settings.
But even if it didn’t convert, Gwenview doesn’t support the Wayland color management protocol (and neither do GIMP, Firefox or Okular). The only two apps I’m aware of that support it are very recent versions of Chromium and Krita. I think mpv may support it as well, but haven’t looked at the code or checked if it actually works as intended.
On Wayland, when you set an ICC profile in KWin, any app that doesn’t explicitly support Wayland color management will have its colors clamped to sRGB by the compositor, so when you open a Display P3 image in let’s say Firefox, what you’re actually getting is an sRGB-clamped version. Gwenview seems to use Qt’s QImage::convertedToColorSpace(QColorSpace::SRgb) for its conversion, and then gets its surfaces sRGB-clamped by KWin. 
That’s probably why it looks different.
If you want to view wide gamut images with correct colors on Wayland, you can use Krita or a Chromium-based browser (I wouldn’t bother with anything older than Chromium 144 due to multiple bugs).
There’s also a way to disable this sRGB clamping in KWin by setting the System Settings -> Display & Monitor -> sRGB color intensity slider to 100%. You’ll get oversaturated colors on a wide gamut display, but then you can create sort of a “delta” ICC profile (created while your display profile is loaded in KWin, keep it loaded afterwards) and load it into each app that supports it (e.g. Firefox, digiKam/showFoto) to get more or less correct colors for casual viewing.
