1.) Verify that the correct X11-property is available with:

  xlsatoms -name _GNOME_BACKGROUND_REPRESENTATIVE_COLORS

If you don't get a reply from that command (it just returns to the prompt) any
notification you trigger (step 3.) will have a dark grey background.

2.) Right-click on the desktop to bring up the context-menu and select the
change wallpaper menu-item.

3.) Trigger a dummy notification with:

  notify-send "Test" "This is just a simple test." -i info

Note the tint of the notifications background and wait for the notification to
close (don't keep the mouse-pointer hovering over the notification).

4.) Change the wallpaper to an image with an overall different tint as the
current one.

5.) Repeat step 3.)

6.) The tint of the notifications background should now be different.
