I had a funny idea yesterday and patched this today. A four octave keyboard is used to enter new pitches based on the last pitch played and the newest note's distance from middle C.

There's a visualization keyboard above the one used for input.

The yellow note represents the relative pitch you would need to play to return to the note you last sounded. Choosing the green notes seems to return to notes you've played in sequence recently.

It's a bit fun to play.

I wonder if anyone is using a similar scheme with alternative tunings. It might be fun to use with microtonals.

It's attached
onionskinkeyboard.pd

Updated with visuals sent to the input
onionskinkeyboard2.pd

Love it! You might consider adding a feature so that you can reset the mid-point from middle to some other note.

Yes!! Moving center note is great! I've updated it:
onionskinkeyboard3.pd

It's interesting to set the center note to a g#/ab.
I didn't implement it too thoroughly, so setting the center note to something other than c crops off the onionskin display a tiny bit on either the top or bottom of the four octaves. Or wait, maybe it doesn't... It doesn't!

I also added a display that keeps track of the center note so you can keep track of a root note.

Once I get my midi keyboard up again I will post a version that will allow the use of a physical keyboard and midi output to use with other sound sources. Think I'll set the note length to mod wheel.