What distinguishes a special flashing light?

A special flashing light is characterized by its specific color and the pattern of its illumination. In the context of the choices provided, the option referencing a yellow light with an arc of 180-225 degrees accurately defines what is recognized as a special flashing light. This particular light is used to indicate the presence of specific types of vessels, such as certain types of fishing vessels or towboats, and is often employed in situations that require special attention or caution.

The 180-225 degree arc is also significant, as it allows the light to be visible from a substantial portion of the horizon but not necessarily from all angles, indicating a specific operational status of the vessel. The yellow color adds to the recognition factor, helping to differentiate it from other navigational lights which might be red, white, or green, thus aiding in navigation safety.

The other options do not conform to the definition of a special flashing light under COLREGs standards. For instance, red and green lights typically indicate the port and starboard sidelights of a vessel, while a white light might indicate the stern or all-round lights. Therefore, the uniqueness of the yellow color and the specified arc range in the correct choice sets it apart as a special flashing light.