Background colour

[Aged P]

If you select a colour with the eye dropper and then just touch the eye dropper on the area around your canvas the colour changes instantly. No key presses required.

I suspect this shouldn't happen but it's very useful.
I did it accidentally to start with.

[DaveRage]

That's an "undocumented feature" *cough*

Basically it's because we treat alt+click and the eyedropper tool in much the same way. And you're correct, it wasn't intentional. I'm also finding I rather like the way it works :)