Hmm.... I believe you on cab units... but hood units were often different.
The EMD F series usually had a red light offset to one side of the rear door, and often the red light in an A unit was in the same housing as the main headlight.
Yeah those red lights were "end of train" lights. Classification lights were either white or green. Marker lights, well that's another ball of wax...
All of this gets pretty specific by road.
That article that lumped the end of train lights with the green and white classification lights is not really correct.
Classification lights
marker lights
end of train lights
3 categories of use, and colors. This is the best I can come up with over the years.
Here's a UP specific article, and they make the point that red lights are not classification lights.
All in all, I see it made sense to allow the lights that were mainly (originally) for classification lights to have the red option. I would suspect that on cab units, nowadays the red gets used way more often that white or green.
I'll have to look up the EMF F3, 7 etc. and see if this was ever true... and I cannot find evidence of the class lights on an FA-1 ever being able to go red, but I would not rule it out.
Here is a variation I had not seen:
Greg