2.) the reflection of the water from the sun, thus why it is only blue during the day.
Don't want to be rude but this is false :S
As a photographer I studied light sources and basically everything I need to know about the sky.
But here are some info from my coursework from last year:
The blue colour of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air.
However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue.
As you look closer to the horizon, the sky appears much paler in colour. To reach you, the scattered blue light must pass through more air. Some of it gets scattered away again in other directions. Less blue light reaches your eyes. The colour of the sky near the horizon appears paler or white.
But a simple way of putting it is: That the gasses in the sky are not fully transparent and the have a blue tint do them :S