Which is the longest current known as "Black Current" due to its black colour?

The Kuroshio, one of the three largest of the world’s ocean currents, has long fascinated humans. The Japanese named it Kuroshio, or black current, for its dark, cobalt blue waters. Physical oceanographer Steven Jayne said, “The Kuroshio is the strongest current in the Pacific Ocean, and is also one of the most intense air-sea heat exchange regions on the globe. It influences climate as far as North America.”