Which color is NOT typically used for a marker on a train?

In the context of train operations and safety, specific colors are designated for markers to convey important information to train conductors and engineers. Red is commonly used to indicate danger or stop signals, while amber often signals a warning or caution, and orange can denote maintenance or work zones.

Blue, however, is not typically used as a marker color for trains in standard operating procedures. It does not convey standard warning or alert messages associated with train operation. In general, the use of blue in rail signaling is very limited and does not serve the same functions as the other colors. The preference for colors like red, amber, and orange aligns with well-established safety protocols across the rail industry.