This uses the same full-sized highlight as used in list view and details view as well as by the file dialog and similarly by Folder View.
The decision to only highlight the label and then custom-tint the icon has been controversial from the beginning and has been carried over from the Oxygen days.
I think after more than five years of being like this, we should re-evaluate whether this is still the look we desire.
BUG: 309722
FIXED-IN: 18.12.0