You are able to directly affect the label.text and label.icon.color properties of a menu tree item through styling, even without the label.icon.color property existing. However the navIcon.color property is not tied into the style in the same way, but that feels more consistent and would add benefit.
If you set an items style class, it affects both of those colors, but does NOT affect the navIcon color, that can only be affected directly, unlike the label icon color. I am not sure if this is intended behavior, or a bug, but it would be nice if the navIcon fill color was tied to the overall style of the item the same way that the label.icon.color is. This would allow you to set a style class for the currently selected page, highlighting that item and changing the colors to match, without having to manually change the navIcon fill color as well.
Edit: I am in the 8.0.15-Snapshot but this has been the case since the initial 8.0.13 nightlies as well.