It's not blue. It's actually black. the 'near' sky is showing the reflected blue color of the oceans in our atmosphere. The true color of the sky is the blackness of space. Is it dark where you are now? Look outside. what color is the sky?
Not reflected oceans. If you think about the earths atmosphere acting like a prism, (or a piece of cut crystal) the angle of the light from the sun enters the atmosphere at the blue angle of the spectrum.
It is nothing to do with reflection of the ocean (the ocean reflects the blue light from the sky, not the other way round - water is not blue). Nothing to do with the angle at which light hits the atmosphere.
Just pop this question into Google for a full and complex answer. In short, the gases in the atmosphere let some wavelengths of light through (red, yellow...) But they 'scatter' blue. As the atmosphere 'throws' blue in all directions in the sky, and this light then reaches our eyes, we see the sky as being blue.
Of course the colour of the sky changes dependant on changes in the composition of the atmosphere above you and the position of the sun (light having to travel through more or less atmosphere).