New highlighting option

[NickIst]

Can you add option for highlighting if there is no RG tags for albums or tracks?

[redwing]

If a field is not available for filters/playlists/highlighting rules, then create a virtual tag and use it instead.

In this case, you could create something like

$IsNull(<Album Gain><Track Gain>,,<Album Gain><Track Gain>)

And then create a highlighting rule that the virtual tag has no value.