(1) Can I change the UI so it more accurately looks like sheet music? I think if it were black and white it might speed along the sight-read skill development.
(2) Can I set more than one part to the right and left hand in the MIDI? It seems like you'd definitely want to be able to do this to play any MIDIs... I have many MIDIs that have the melody split into like 4 or 5 different parts...
That's a good question. It's down to a personal taste I suppose. You can configure it the way you like it. Including any background image (or none at all), and also any color combination of your choice.
It is already included out of the box several themes without any background images. In the preference, there is a dialog for changing colors for each theme (and preview them using Apply button).
You can also configure a many of them as you like and switching between them as you wish.
and thanks for your answer. Those seem like nice features. Are you maintaining a fork of a fork of Piano Booster? Would you consider incorporating my revision of the Swedish strings I submitted to the original Piano Booster via Weblate?