Ok, there are 2 settings in the color.ini of a scheme that should deal with the road color ahead and behind the vehicle:
planned_road_visited (behind) and planned_road (ahead). That's what I already knew.

If I change planned_road, the color changes to what I am expecting. This works perfectly.
But If I change planned_road_visited, nothing happens. Then road already drive past is displayed in the same color as the planned_road is set.

So what am I missing?