I've already searched a lot regarding this topic and it honestly seems impossible.
Which is a bummer, since being able to add some small details/artistic touch to this bland area would definitely be very welcome.
Unless I am mistaken and there is a way to do that - please, enlighten!
Afaik no, since it is provided by the app, not by the html code. All scrollviews have this behavior enabled by default. However a image as backgroundcolor should be visible.