Final answer:
Vessels at anchor are required to display an all-around white light visible in all directions, in accordance with maritime navigation rules.
Step-by-step explanation:
All vessels are required to display navigation lights that adhere to the International Regulations for Preventing Collisions at Sea (COLREGs). These lights include a variety of colors and configurations, designed to indicate the size and type of the vessel as well as its direction of travel and whether it is at anchor. For example, a power-driven vessel moving through the water will typically display a red light to its port (left) side, a green light to its starboard (right) side, and a white light at the stern (rear). Additionally, vessels at anchor will display an all-around white light visible in all directions. It's important to note that these regulations are crucial for maritime safety, as they allow vessels to communicate their position and status to others in the vicinity, thereby preventing collisions.