This extension based on grayscale-all by laerne, found at https://github.com/laerne/desaturate_all .
Installation
Copy this folder to the gnome-shell extension folders, typically under .local/share/gnome-shell/extensions.
Using a terminal, you can do the following sequence of commands :
$ git clone https://github.com/amarovita/tint-all.git $ mv tint-all ".local/share/gnome-shell/extensions/tint-all@amarovita.github.com"
Then restart gnome by pressing ALT+F2, then entering r and validating with RETURN.
You can now enable the extension by browsing to https://extensions.gnome.org/local .