I think the developers have gone a bit over-the-top with all the color/layer mode options. Nothing obvious in the preferences. A very vague memory of something about 0-255 versus 0-100% That could have been the color-picker tool where the info box has both options, but that does not help with the FG/BG color selector.
I had a good search around and nothing that I could find.
Best I can suggest is use the HTML notation which is a little quicker than individual RGB entry.
Using an external converter, you might have a favourite, attached a bash script (remember to unzip it) that runs in a terminal.
Obviously, no good if using Windows
I have this in usr/bin Maybe there is a similar Gimp plugin/script somewhere, I do not know.
Have an RGB value, copy & paste into HTML notation
Want percentage colours to RGB - use HTML value to RGB
I had a good search around and nothing that I could find.
Best I can suggest is use the HTML notation which is a little quicker than individual RGB entry.
Using an external converter, you might have a favourite, attached a bash script (remember to unzip it) that runs in a terminal.
Obviously, no good if using Windows
I have this in usr/bin Maybe there is a similar Gimp plugin/script somewhere, I do not know.
Have an RGB value, copy & paste into HTML notation
Want percentage colours to RGB - use HTML value to RGB