Another way.
The problem with Gimp is AFAIK it does not color-pick outside the Gimp environment.
I can not recall a plugin that allows that, or one that brings up a useful dialog.
You could try a small layer, filled with a FG-BG gradient and color-pick off that. Small so it is movable and of course hide-able. The only snag is moving between layers which might break your work flow. That can be assigned to keyboard shortcuts where up/down layers are unassigned by default.
Edit:
The documentation does say that the color picker will work outside the gimp window but looks like not the color pick tool you get in the toolbox.
A variation on the 'floating layer' An image with the required colours open in some external image viewer application. The one here is a linux Viewnior. (I see you use linux, plenty of small applications to choose from) With the Gimp dialog 'colors' open, the color-picker that comes with that will select from the external image.
The problem with Gimp is AFAIK it does not color-pick outside the Gimp environment.
I can not recall a plugin that allows that, or one that brings up a useful dialog.
You could try a small layer, filled with a FG-BG gradient and color-pick off that. Small so it is movable and of course hide-able. The only snag is moving between layers which might break your work flow. That can be assigned to keyboard shortcuts where up/down layers are unassigned by default.
Edit:
The documentation does say that the color picker will work outside the gimp window but looks like not the color pick tool you get in the toolbox.
A variation on the 'floating layer' An image with the required colours open in some external image viewer application. The one here is a linux Viewnior. (I see you use linux, plenty of small applications to choose from) With the Gimp dialog 'colors' open, the color-picker that comes with that will select from the external image.