Note: This has been confirmed to work with LightDM.
Users of display managers might experience a flickering during the transition between the display manager and the Openbox desktop. The flickering comes from Openbox setting the root window's color during startup. Therefore there is a brief moment when the display flashes in a grey color, between the display manager's background and the desktop's wallpaper.
Setting the root window's background
color can be disabled by editing the Openbox startup script found in /usr/lib/openbox/openbox-autostart. Simply comment out (or delete) the block starting
with # Set a background
color.
Note: Users who do not specifically set their wallpaper will "inherit" the display manager's background automatically if they disable the root window color adjustment.