Coloring adjacent notes by interval

[Michael Käppler]

Hi all,
I would like to color all successive notes in a voice that span a
certain interval, like e.g. a perfect fifth upwards.
Seems to me the most straightforward and extensible way would be to
write a scheme engraver for this, right?
Does someone know existing examples of scheme engravers that I could
look at as a starting point?
I am somewhat confused by the different hooks
(start-translation-timestep, acknowledge-music etc.) and where
to do which kind of things.

Kind regards,
Michael