Omnioutliner: Individual row background

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.

Select the rows and then ‘show’ the inspector (Comm-Shift-I). In the ‘Paragraph’ section, click the ‘Background’ dropdown and choose your colour. Note that the colours blend if you use less than 100% opacity, so take that into account.