Highlight unplayable notes for diatonic instruments

Your idea

For diatonic instruments (instruments that can only play notes from a certain scale), notes that are not in its scale and therefore unplayable should be highlighted - in the same way that an instrument's range can be defined, and notes outside of this range are coloured red.

I can imagine an extension of the distinction between amateur/professional range - notes that are easily playable vs. notes that are technically possible but more challenging to achieve. Would need to be able to define which notes fall into which categories for each instrument.

For example:

• A D tin whistle is diatonic in D major. Notes in the D major scale are all playable, as well as C natural. All other notes are possible using half-hole fingering, but much more difficult, so would be highlighted as 'professional'.
• Certain types of accordion and concertina are diatonic in one (or more) keys. All notes inside of those keys are playable, but any notes outside are impossible, so would be coloured red.

Problem to be solved

When working with diatonic instruments, an immediate visual indication of whether any notes are unplayable (or difficult to play) would help save a lot of time and avoid writing un-idiomatic parts.

Prior art

No response

Additional context

No response

Checklist

• This request follows the guidelines for reporting issues
• I have verified that this feature request has not been logged before, by searching the issue tracker for similar requests

No files, tests, or entry points are named in the issue. Start by locating the existing instrument-range highlighting behavior, then determine how instrument scales and playable or difficult notes are represented. Done should include visual highlighting for unplayable and technically difficult notes on diatonic instruments, with definitions that support the examples described.