Hi again,
Thinking about this some more, I realized that there is a bit of redundant calculation going on: the pitches to be colored are extracted each time the function \colorPitches is called. While the wasted time probably wouldn't be noticeable with the two or three notes a handbell player would have in circulation, it bugs me. It might be noticeable if you were to do something like color the range held in common between two instrumental parts--don't know why you'd want to, but there it is.
The attached uses a new function \extractPitches which returns a list of the pitches used in a music _expression_. This might be useful for other purposes.
[BTW, there's a correction in extract-pitches.]
HTH,
David
color-note2.ly