Something I noticed when I was watching some photos: Nearly all Brittish trains have an orange roof line. Now I wonder for the use of this line. Is it reflecting in the dark or something, for better visibility?
I seem to remember this coming up a few months ago.
The full Group Regulations document entitled "Overhead Line Equipment (OLE) Warning Line on Traction and Rolling Stock" can be found here (although note the actual URIs on this site have a habit of changing frequently). This document will tell you all about what the orange lines are for and what stock is required to carry them.
To sum it up the only stock that aren't required to carry the orange cantrail warning are:-
• vehicles with route acceptance limited to lines NOT electrified on the overhead system (for example classes 450, 444)
• steam locomotives