Bem, isso funciona para mim:
Run regedit and navigate to:
HKEY_CURRENT_USER\Control Panel\Colors
Right click on the "colors" key and make a backup (export the reg key).
Then in the right pane scroll down to window - double click and change the value to 200 200 200
Exit registry editor and log off then log back on again. You'll see a background like this:
Crédito: link