[Background] several issues

[diver]

*1. Monitor image gets corrupted if you move another window above it. *2. If you set background color for current workspace and the switch workspaces several times you should see that background color isn't properly updated in others workspaces. *3. After clickong Apply button, Revert button should be disabled. *4. ColorControl size is bigger than bbox. *5. Apply button should work if you set background color for current workspace and the switch to another one and select "All warkspaces" from menu.

Feature request: ouble clicking preview image should bring up Screen pref.