When adding a song, why are some on a grey background?

[JerryK]

In Setlist Songs | Edit Songs | Add Songs dialog box, whether showing a filtered list or not, the list shows some songs on a grey background.  Why is this?
Thanks

[arlo]

Those are songs that are already in the set list. This doesn't stop you from adding the same song again if needed, but it reminds you of what songs have already been added.

[JerryK]

Cool. Thanks