Highlight now playing tracks

[Nubi]

Hello, I would like to highlight the tracks from the now playing list in the libary (highlight column).
For recently played tracks this can easily be done with a rule. Also tracks from the same Album can be highlighted with a rule. There are a lot of posibilities...But I don't have a glue how to highlight exactly the tracks which are on the the now playing list.
Does somebody have an idea?

Thanks in advance!
Skamander