Setting TextView background color?

Is there a way to set the background color of a `TextView` wrapped in a `BoxView` to some other color than the default / transparent?

I tried:
- Providing a StyledString with a background (sets only the background of the string, not the entire area)
- Looking for setters on TextView; there's a way to set the 'eeffect' but not the background
- Looking at `Layer` which fills an area with a background: but I found no way to set which color