(5 hours ago)Jānis Wrote: Thanks, putting it in "~/.config/Cyan/icc/" worked!
Only, when I open the converted file in GIMP again, "the out of gamut" marker still paints about the same areas as out of gamut than before the conversion. Shouldn't converting to CMYK get rid of all unprintable colours?
The Gimp 2.10 softproofing is a preview of what to expect when printed using the specified profile. Using Cyan plugin just creates a color-separated CMYK file. You might see some change if you open the original then open as layers the cmyk file. Although Gimp is 100% RGB so the cmyk image is converted.
If you want to lose the out-of-gamut values then before using cyan, use soft-proofing and adjust the color curve until the out-of-gamut marker vanishes. This more like the actual printed result.
This example a bit extreme, usually a small adjustment on the bottom left makes a big difference.
I would just leave as-is. Generally the printer does the correction. and accept that bright colours become dulled.