Final answer:
The color of the vest worn by the Seattle police on the ferry would depend on the specific uniform policies of the Seattle Police Department at the time.
Step-by-step explanation:
The color of the vest worn by Seattle police officers on the ferry would depend on the specific uniform policies of the Seattle Police Department at the time the question is referring to. Uniforms can vary in color and design between different police departments and even within different units of the same department. To accurately determine the color of the vest, it would be necessary to reference official documentation, photographs, or videos from the time period in question.