Test outputs button

[SourceChild]

Make a screen shot of your configuration. Then make it your wallpaper. See the example I'm using at the moment. Then when you exit the HUD, you see an accurate test pattern.

[kiwi]

Yes that's an option, but it's still not a quick solution, and you still have to remember to set your desktop back to black.
It also doesn't avoid the other two outputs going out of full screen when using a triple head.

Thanks for the suggestion however.