We know that sky color is due primarily to Rayleigh scattering. Is Rayleigh scattering the dominant effect for ocean color too?
Rayleigh scattering is also present in water, but the main reason of the blue color of the sea is absortion, due to vibrational transitions.
It looks like Raleigh scattering also makes an indirect contribution to the sea color, as "the surface of the water reflects the color of the sky" (http://en.wikipedia.org/wiki/Color_of_water )
When white sunlight enters the large masses of water the water molecules absorb most of the higher wavelengths in the red, green and yellow parts of the spectrum by vibrational transitions; they also absorbs blue but emit it immediately (Rayleigh scattering) so the ocean water looks blue.
We can say that both Raman scattering (scattering by vibrational transitions) and Rayleigh scattering are combinedly responsible for the blue colour of the ocean, yet some of its other colors like green and red are due to plant life, algae, and other factors like rocks, minerals etc.
Because Raman scattering is a weak effect, it involves only 1 out of 10^9 photons so it requires huge masses of water to manifest properly: a glass of water, a river, or a pond water will appear colorless.