This is an early mockup for the keys. This still has a long way to go before it will be a "real" screenshot, and some things will be infeasible to do in the time I've got. For example, the white key reflection on the black keys won't actually match the blue/green/etc. colors like it does in this mockup. Also, the wood above and below probably won't be as pronounced (or there at all) in the final result.
Still, this is sort of what I've got in mind. I'll post more mockups of the "active" black keys, notes, and revamped particle effect as I work on them.
I took a realistic approach to get this far: measuring all of my test keyboards with a tiny steel ruler down to half-millimeters and then modeling the result in 3D. It's different than the more iconic approach other apps take (e.g., GarageBand's extra-rounded corners on the white keys). I'm curious to hear what you think.