Support changing the underlying VD background color.

I can't see a way to change the color of the background on any virtual device. is this possible?

I have created some nice switch sets on virtual devices but they all have black between the keys. Fine when things were just colored square keys, but now we can use images as key backgrounds it would be great to change the color of the underlying background as well. This way I could mount my switches on, say, an Airbus blue/grey background with unused buttons showing up in a color more fitting to that aircraft. Even better, if I could add an image, then I could have buttons on a wooden-backed virtual device for, perhaps a Tiger Moth.

markcellis / X-KeyPad

Support changing the underlying VD background color. #84