Willi is right, that is a fixed part of GE. I, too, have been annoyed more often than I can count by the similar color of roads and borders! As I recall, the road lines are wider than the border lines, making for further confusion, at least for me.
The only user-changeable line is the "Path" feature on the toolbar, at the top of the screen.
What is this life if, full of care, We have no time to stand and stare. - W.H. Davies, from "Leisure"