The Santa Fe used amber instead of green.
In addition to what has already been said, when stopped on double track or running the 'wrong way' (against the current of traffic) on double track the inside rear marker was green, while the outside was red.
Greetings from Alberta
-an Articulate Malcontent
This is the full rules for end-of-train markers from the 1962 Canadian UCOR, I expect it was the same or similar on all or most US railways as well (except for examples cited above like ATSF using amber instead of green).
19. MARKERS – the following signals will be displayed to the rear of every train to indicate the rear of the train. By day – markers not lighted. By Night:On single track and when running with the current of traffic on two tracks, markers lighted displaying red to the rear.On two tracks, when standing or running against current of traffic, markers lighted displaying red to the rear on the outside, and green to the rear on the inside. On more than two tracks, when running with the current of traffic, or when standing or running against the current of traffic, markers lighted displaying red to the rear unless otherwise directed by special instructions. When a train is clear of the main track to be passed by another train, lighted markers will display green to the rear. When the rear of a train is equipped with built-in markers, they must be lighted by day and by night. When a train is equipped to display a single flashing type marker it will be unlighted by day; by night it will display flashing red to the rear, except when clear of the main track to be passed by another train it will display flashing green to the rear. EXCEPTION: The requirement that markers display green to the rear when clear of main track does not apply in CTC.
19. MARKERS – the following signals will be displayed to the rear of every train to indicate the rear of the train.
On more than two tracks, when running with the current of traffic, or when standing or running against the current of traffic, markers lighted displaying red to the rear unless otherwise directed by special instructions.
When a train is clear of the main track to be passed by another train, lighted markers will display green to the rear.
When the rear of a train is equipped with built-in markers, they must be lighted by day and by night.
When a train is equipped to display a single flashing type marker it will be unlighted by day; by night it will display flashing red to the rear, except when clear of the main track to be passed by another train it will display flashing green to the rear.
EXCEPTION: The requirement that markers display green to the rear when clear of main track does not apply in CTC.
Chris van der Heide
My Algoma Central Railway Modeling Blog
The N&W only used yellow and red on cab markers.
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The Western Maryland Ry used red to the rear and amber/yellow in the other positions. The markers were able to be repositioned when in a passing siding to show amber/yellow to the rear rather than the red used when running or stopped on the mainline.
oldline1