For text, image, and music frames, it’d be nice to include a color fill component. The feature has once been alluded to by David here, and I’m surprised that it still hasn’t found its way into Dorico.
Currently, I have a file called white.png on my Desktop so I can wipe out some background.
On that note, it seems that if I pick a font that has a border (i.e., an Instrument Change Label), the border seems to be hidden behind the background of the text box frame.