Why sky appears blue in colour
The gases in the atmosphere refract light. Blue is in the middle of the light spectrum and that is why we see blue during the day, and reds and oranges at dusk and dawn, and violet at twilight.
The ozone layer spreads blue light most efficiently that's why the sky is blue
The sky is the reflection of the ocean.
One possible cause could be the ozone in the atmosphere, which can be seen as blue in its liquid state