Fix the VLC screen if it is green or any other single color
VLC, or even the whole monitor of your PC, may appear in shades of green or of some other color, as if it were unable for normal color reproduction.
This can be a problem of your graphics drivers, but before you try to find upgrades or re-install anything, try checking the cable that connects your PC with the monitor.
You may need just to tighten this cable, making sure it is firmly connected in both locations.
Since this is the easiest and fastest way to fix your problem, start by checking the cable, then think about updating your drivers.