I was looking at some old rule books and enjoying the various marker light settings for classes of trains. Then I realized that the aspects might require white, green, yellow, or red or combinations of those colors to designate a train's status properly. Was there a way to change the colors in the lenses, or did the tender locker have extra sets of markers to make a proper display?

The brackets for my caboose markers allow for them to be turned 90 degrees to display green. I suspect the lanterns on the Engine worked similarly. When Diesels are so equipped with built-in marker lights they there was a lever you could move to a Left-Right position to change color.

I'm familiar with steam locomotive classification lamps. They're attached to the smokebox next to the smokebox front, or sometimes on the smokebox front itself, either at the 2 o'clock and 10 o'clock positions, or - on small engines - at the 3 o'clock and 9 o'clock positions. Pyle-National classification lamps (the "cannonball" design) have a lever to switch between no color filter (so lamp shows white) and green color filter glass. White was the equivalent of a white flags - train running as an extra, so not in the printed employee timetable. Green indicated that one or more sections of the same timetabled train were following this train.

- Doug Debs

Doug Debs is correct about the two aspects of the Pyle-National steam locomotive classification lights, there was technically three indications, off, white or green. Off indicated a single scheduled train, with no sections following. But that was the indications for a forward-facing locomotive on or off a train.

The author was asking about other color indications, which might include yellow.

I'll specifically address N&W and VGN. Disclaimer, this is devoted to operation at certain time frames, your mileage may vary! But a yellow indication, was used on those roads. It was most specifically for running light in reverse or in use as a pusher on the end of the train. It was specified in the rule book for the rear of the train, displaying either yellow color markers or yellow flags on the rear of a train. In the case the railroad would use rear marker lights, either sitting on the pilot (at night) or yellow flags in the coupler, or on the flag holders on the smokebox.

Hope this is helpful

Best
Ken Miller

In all the old catalogs I've never seen yellow as a option for locomotive class/marker lamps. White, green and red. The two color lamps could be rotated, or have colored glass plates installed, or a "flip lens" internally. The three or more lights either had colored glass plates that could be installed inside the clear lens, or the more modern lamps had an external lever you could push that would flip the color you needed into place. Of course, following failsafe practice only one color could be moved into place at a time.

As has been done a couple of times before on this sight, You all are once again confusing Class lights and Marker lights. They are two very distinctly different things and unrelated.

The long, drawn out traditional version of the official definition of a train usually included part or all of the following:
Train: A locomotive, with or without cars, displaying markers and authorized to move on main track.

Individual RRs changed that a bit by omitting or occasionally adding parts. Class and right of trains are rules or TT instructions. Rules for the proper display of Markers and Class lights are separate rules and in the old days there were often multiple rules for Markers.

Marker lights are, as the name implies, to mark the rear end of the train/movement. In early times before there was any standardization, RRs made their own specific determinations on colors. The rear-facing marker color could be red, green, yellow, purple, white or even lunar white. The DRG in it's early years used green for markers and at one time their rulebook specified both green to the rear in one rule and red in the very next rule. So??? Later standardization started (and eventually gov't regulation) and everyone switched to something in the red/orange/yellow spectrum. That color was/is required to be displayed to the rear. The alternate color displayed to the sides/front is RR-specific and not regulated so the RRs could do whatever they thought prudent to their operating situation, but usually ended up either yellow or green. There is some thought that yellow is better than green, since in some instances a marker lens could be confused with a lineside track signal at a distance and yellow is more restrictive so less likely to be misinterpreted as a 'Clear' signal and cause a bigger problem.

Class lights (again, implied by the name) are only for displaying the train's class at the front of the train. While there were probably some RRs that had different colors of their own specs early on, class light use generally started later than markers and quickly went to the traditional white for extra and green for following sections.

A good illustration of the separate nature of class and marker lights is the PRR's 1922 adoption of the 'clawfoot' lamps on locomotives. See here http://www.railroadiana.org/library/PRRLocoLightPractices.pdf. PRR was using the same physical lamp body for both purposes, but they are not the same lamps operationally. On the front of the locomotive are a pair of class lamps up on the smokebox with white and green lenses for class lights and a pair with red and yellows on the pilot for markers. These markers would, of course, only be for when the locomotive was running lite reverse since the front of the locomotive is now the rear of the train by definition. (It would also be displaying a white light on the rear of the tender since that is now the head end of the movement.)

To the OP's question of changing color lenses - where a caboose or passenger train would operate over different RR's territories/rules, an additional set of marker lamps with the proper colors for that RR's rules would be carried onboard (or supplied by the other RR at the interchange point) so they could be switched out upon entering the other's territory if needed (this, again, is rules-dependent). Lenses were not generally swapped out in the lamp bodies in the field, but in the lamp shops when repairs were needed.

Some railroads at some times did combine marker and class lights in the same housing. Sometimes there were movable filters and a clear or white lens, other times, some of the 4 sides of the housing had different color lenses; either the housing could be rotated or it had extra mounting arms.
Older Multiple Unit cars on the Reading Company had red, yellow, and green movable filters behind the lens, each with the proper colored handle. If all were away from the lens, white could be seen. Dark was the 5th aspect. I don't know what yellow was for.
In some years, Pennsylvania RR used a yellow rear marker on one side of a caboose, to indicate that the train was could be passed on that side. The other side still displayed a red light. Usually the rule was that the red wasn't to be changed to yellow until the train was clear of the switch and it had been reset.
TAN: On Philadelphia & West Chester traction, there were separate green, yellow, and red lenses, each with its own bulb. Green was front of a regular car, yellow was front of an extra car, and red was for the rear. Newer cars had only red and green.

All of my research indicates that TrainDetainer is 100% correct.

I will add that certain railroads that shared track but had different operating rules regarding display of markers sometimes equipped locomotives or cabooses to accept multiple sets of lamps for the purpose of complying with the other's rules while on their track.

A few years ago I purchased a set of electric class lamps which are capable of displaying white, green, red, or amber to the front and to the side (simultaneously). I was my curiosity about what circumstances would require all of these in one housing that caused me to research via old RR rule books to find examples of rules requiring the display of green and/or amber on the rear... typically one or the other for the whole railroad. As mentioned the Pennsy was one, others included the Ann Arbor, and C&O.