Custom panel background color

[DarkAnturian]

There could be a way to have only the keys show up, like you can transparent the background out but keep the keys filled in?

[RoanH]

Mhm, this could be a thing yeah. I'll most likely not do this for the next release, partially because #43 can yield the same result given a bit more effort. But I do like the idea of separating the inner colour of a panel from the colour that's used to fill the area between panels.