I may have the solution for you, but to test if it will be the solution for you, then do the following:Right-click at your desktop, choose "Settings", then "Compositor" and "Disable Compositing". If the icons now look as they are supposed to, then enable compositing again (Settings-Compositor-Enable Compositing).Does the icons still look good?
Maybe try turning off compositing? That helps keep the CPU use down a bit, in my experience. Go to Openbox (right click on on the desktop) menu, Settings, Compositor, Disable compositing. Remove the compositor from the Openbox autostart file (Settings>Openbox>Edit autostart) to make the change permanent.Hope this helps