I figured that level design is going to be a big part of this project so I wanted to get an easy way to express levels as json strings very early on.
So the first version level designer is just a big text box and a live interpretation of the JSON expressed in the box. So you can live edit the JSON and change the features of the level.
The physics and collision model is working well and looks natural (although doesn't do color-physics yet).
All this currently works here http://elementalsystems.github.io/PhaseBall/levdesign1/ (you need to press the start! button once)