When using the play buttons, going with the small color shift makes it less than obvious what is playing. Changing it to a stop button instead of a colored play button would be more consistent with user interface practice. It is especially confusing on the Browse page where there are 4 play buttons to choose that might have been played.
Similarly with something that looks like a record button for capturing and detecting midi and audio is not very obvious. Then going to yet another record button that looks disabled rather than armed and switching to a flashing icon is a bit non-intuative.
Also a bit of branding on the interface to tell whether it is the AU, VST, Scaler Conrol, or the Scaler Audio would be more clear when looking at them.