‘Default color’ is not just a shortcut for color, its behavior is different from other colors’. I think ‘Default color’ is not the specific color but an attribute for inheriting the color from its parent.
This behavior seems to be same on older versions of Cubase (I checked it on 6.5, 7, 7.5, 8, 8.5 with clean settings). On Cubase6.5, default color is not changeable. They are all grey.
The fact that ‘Default color’ track head indicates the color defined in Preference (not the inherited color) may have been confusing users. It should be called ‘Color for inherit mode’ ‘Color for follow mode’ or something like that.
Old similar topics
Events default wrongly to folder colour
Is this intended? Auto coloring issue