Why did the color of the California current change when it became the North Equatorial Current?

The Kuroshio also known as the Black or Japan Current (Nihon Kairyū) or the Black Stream, is a north-flowing, warm ocean current on the west side of the North Pacific Ocean. Like the Gulf Stream in the North Atlantic, the Kuroshio is a powerful western boundary current and forms the western limb of the North Pacific Subtropical Gyre.
I hope it’s understandable to you?

The correct answer is c