When might a guide use the intercom to report "The YELLOW light is out at station ______?"

In the context of a cave tour, the guide using the intercom to report "The YELLOW light is out at station ______" specifically indicates a maintenance issue. The yellow light serves as an important signal related to the safety and operational status of the tour area. If it is out, this can signify that there might be a problem that requires attention, which is crucial for ensuring the safety and comfort of the tour group. Identifying and reporting such maintenance issues proactively helps to prevent complications that could arise if the situation is ignored.

In this instance, the other options do not align with the typical use of the intercom for reporting a change in the status of lights. While emergencies or discomfort may necessitate communication, reporting a light being out is most directly related to the need for maintenance to ensure the tour operates smoothly and safely.