What's a simple "colour picker" app for GNOME?

gpick

That's strange that you couldn't install gpick, as I get the following :

apt-cache search gpick
gpick - advanced GTK+ color picker

I suppose it could be in a source that you currently don't have enabled..

To pick a colour, launch Gpick, lcick on the swatch, and then press space when your mouse hovers over the colour you want to record.

gcolor2

That being said for simple colour picking I prefer gcolor2 - Nice and simple to use and should do exactly what you require.

You can install it with following command:

sudo apt-get install gcolor2

I like to use the software agave. It's a simple software that gives your color combinations, and it has a color picker.

sudo apt-get install agave

Worth give it a try!

Regards

grabc is as simple as it can get. Spawns a cursor, outputs color on stdout when you click. Pure Unix way.

$ grabc
#f47276
244,114,118

To install it, run sudo apt install grabc.