There may be a simple way to do this but, if so, I can’t find it.
What I want to do is colour the background of some individual rows, but not all at the same style level. For example, I may have 30 rows at level 2, but I only want to highlight 6 or 7 different rows so that those particular ones, dealing with a particular topic, stand out from other rows that do not deal with that topic.