For the most part, class lights on the front of locos most often were not lit. That's because just about every train was scheduled, be it freight, express or passenger.
The only time the class lights were used was if a train was running 'extra'. That meant
it was not in the timetable and was running under written orders. The class light color would be white or clear.
If a scheduled train was running with more than one section, all sections running ahead of the last train would show green class lights. The last train of the sections would not show any class lights, because it was THE scheduled train, running in its assigned time table slot.
Red was not used as a front classification light. Most RTR locos have them because they 'look nice.'
Red was indeed used for tail end marker lights. They were only on the rear end of a train, to mark its end.
The rear marker lights could also show combinations of amber and red or red and green according to individual railroad rules. Those set ups were generally used when a train took a siding. The color would be changed on one side to show it was in the clear for any overtaking train approaching from the rear and mark the clear side.
Ed B