What causes the colour of the ocean?

The colour of the ocean is primarily determined by the absorption and scattering of sunlight. Water absorbs colours at the red end of the light spectrum and scatters shorter wavelengths, like blue and green. The deeper and purer the water, the bluer it appears. Algae, phytoplankton, and suspended particles can also influence the colour, making the water look green, brown, or even red, depending on the concentration of these organisms. Coastal waters, for instance, may appear lighter due to the presence of sand or sediment.