White IOBoxes?

I am using vvvv for some time now, but I now I saw in Diki’s , awesome, gesture module, he uses Black/White Ioboxes set to toggle.

How he does that?
Or even better, How do I do that?
(talking about the color, not the toggle ;) )

theres a hidden pin “show background”.
indeed its the first time i saw someone using this feature…