Monitor is turning green, how to fix it?

I recently repaired my monitor by replacing some capacitors on it. After being successful with that a friend of mine started having a problem with his monitor, so I said I'd give it a look. Its not the same problem, hes seeing green discoloration, looks like green powder all over the screen. The monitor is an LCD, and it doesn't seem to be a cable issue as we've tried a different VGA cable, however when I tried using the HDMI port, i saw the problem but then after a minute or two it went away.

So maybe someone can help me diagnose the problem, or if its the green gun, can i fix or replace this? I visually inspected the capacitors on this monitor and they seem fine, but I'm told that its not always visible when they're screwed up... can I test them?