Question

y sea looks blue??

Answer 1

I guess for the same reason the sky looks blue :P

Answer 2

Reflection of sky

Answer 3

http://www.loc.gov/rr/scitech/mysteries/oceanblue.html

Answer 4

white rays from the sun fall on the surface of water in the ocean and most of the longer wavelengths aer absorbed and the short wavelenghts are scattered away. The amount of scattering is inversely proportional to the fourth power wavelengths. Hence the short wavelenghts are scattered more than the long wavelengths. The scattered blue light reaches our eyes and the sea looks blue.

Answer 5

simply reflection off the sky. I think that Rayleigh's diffusion that krishnakumar123 has talked about concerns only only the color of sky.