Macbook Air HDMI green display bug

The problem:

Macbook air connected to an external monitor via the mini display port using a displayport to HDMI cable; when watching videos such as youtube in full screen, after 5 seconds of not moving the mouse, the display would go all green, including the black parts of the screen.

The diagnosis:

This is most definitely not a cable issue, nor a screen issue, as multiple cables and screens had the exact same issue. It was an issue with the macbook air, but because moving the mouse again would instantly fix the crazy green colour, I thought it must be a software issue with regards to the power output to some component. It also doesn't occur if the lid is open on the macbook.

The fix:

I thought I had fixed it by going to

Settings > Energy Saver > Power Adapter > [UNCHECK] "Prevent computer from sleeping automatically when the display is off".

But after restarting it's broken again