The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light . These are more effective in scattering light of shorter wave length at blue end.
This scattering blue light enters our eyes and makes the ocean and sky appear blue.
The phenomenon is called 'Releigh scattering ' .This scattering refers to the scattering of electromagnetic radiation by particles of much smaller wavelength.
These shorter wavelength correspond to blue hues, hence that's why when we look at the sky, we see it as blue.
Blue light is scattered more than other colours because it travels as shorter , smaller waves.