Following up a bit late to the discussion I have copied the pertinent Rule 19 diagrams shown below pages 32-37 from the D&RGW 1924 Rulebook. I believe this Rulebook would have been in effect on both RGS & D&RGW until the Jan. 1, 1938 Rule Book was released which no longer required a cupola light ( the 1938 Rulebook was also when the side and front facing caboose marker lights would have changed from Green to Yellow). So the answer to the original posters question: prior to 1938 the light box would have displayed no color signal during the day and at night green toward the engine and red to the rear (Rule 19) except when on a passing siding green also was to rear. From 1938 on if the cupola light box was still in place it would not have a lantern / color light displayed and would just be clear glass showing (which is also correct for pre 1938 daytime running).
Rod
Edited 1 time(s). Last edit at 07/05/2012 06:44PM by rod.