Edit: Sorry, just read the post again and you are using Gimp 2.8.14 That is a very old version of Gimp. The screenshots I gave are kubuntu Gimp 2.10.12
Edit again. DistroWatch lists Manjaro 18 as using Gimp 2.10.8 The first thing you should do is check the Gimp version and update from the Manjaro repo or ask about it on the Manjaro forum
https://forum.manjaro.org/If the Manjaro repo does not have a more up-to-date version then it might be possible to run a portable Gimp, an appimage from
https://github.com/aferrero2707/gimp-appimage/releases/ (click on assets for the list)
However, not too sure that gutenprint will work with latest versions
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Nothing very automatic.
I would start off with Edit -> Preferences -> Colour Management. Helps if your monitor is profiled but still put in the printer/paper profile for soft-proofing.
https://i.imgur.com/jrkSb2e.jpgThen for any open image you can change the profile if needed Image -> Color Management -> Assign Color Profile.
https://i.imgur.com/sllZudg.jpgEnable Color Management for Soft-Proofing. View -> Color Management -> Color Manage this view....etc...
https://i.imgur.com/cApiDuw.jpg to fix (or ignore) any out-of-gamut colours
Nothing much to do in Gutenprint, except it is worth running some test prints off with various settings. Compare with what is on your monitor. I know because this laptop display is not profiled, prints come out dark. So I bump brightness up by a small amount.
https://i.imgur.com/Hb8coaE.jpg