Yes I have added all these:
<element id="NowPlayingList[TrackDetail].ListHeader" bg="40,240,240" bg2="225,5,5" fg="0,210,0" bdr="255,80,80" />
<element id="NowPlayingList[TrackDetail].Default" bg="55,255,255" fg="0,200,0" bdr="200,2,100" />
<element id="NowPlayingList[TrackDetail].Highlight" bg="45,236,172" bdr="227,216,152" fg="0,220,20" />
<element id="NowPlayingList[TrackDetail].Lowlight" bg="35,235,235" bdr="25,105,25" fg="0,250,40" />
<element id="NowPlayingList[TrackDetail].Disabled" fg="70,70,0" />
<element id="NowPlayingList[TrackDetail].ListAlternating.Default" bg="48,248,248" fg="0,210,0" />
<element id="NowPlayingList[TrackDetail].ListAlternating.Disabled" fg="70,250,170" />
But it appears none of them changes background of only track that is now played.
Default and Alternating change color of rows. Highlight is row that is selected, Lowlight is that was selected but window is inactive and I am not sure what Disable changes.