As information concerning prototype operating practices, regardless of railroad:
1) White = Extra train (during daylight hours the locomotive would be displaying white flags, and at night, white class lights).
2) Green = Second section following (during daylight hours the locomotive would be displaying green flags, at I night the class lights would be changed to green).
3) Red = Rear, i.e. the locomotive would be operating in reverse.
4) No class lights, and no flags = regularly timetable scheduled train.
