Originally Answered: Why is the sky the color blue?
The sky isn't blue, it's black, and the color we see has nothing to do with any reflection of the ocean. The atmosphere just gets in the way, in a manner that when we look up we see blue. This atmosphere is primarily nitrogen-oxygen. The Sun puts out everything from high-energy gamma-rays to low-energy radio waves. They take about 8 minutes for those photons (packets of light) to reach us.
When they do, the high-energy gamma-rays pass the exosphere, get into the thermosphere, but are stopped quite quickly by the ionosphere, which is at the base of the magnetosphere (the field created by our magnetic field, which deflects X-rays and cosmic rays that would kill us). The ionosphere is an area where atoms have had electrons ripped from them ("ionized"), which makes them good at absorbing gamma-rays (which would also kill us, like the other high-energy rays). Incidentally, it's also why we use it to bounce radio signals over long distances. So now the gamma-rays are gone.
The rest of the spectrum continues deeper into the atmosphere, until it gets to the stratosphere, and hits the ozone layer. The ozone layer is to ultraviolet (UV) light what the ionosphere is to gamma-rays. It absorbs them, blunts them, stops them (a neat process, below if you want to know more).
The rest of the spectrum continues on. The low-energy photons, beginning with radio, going to infrared, red, orange, yellow, and even green just blow right through to the surface, where the infrared provides heat (IR light = thermal energy), and the other light provides visible light. So green is gone.
So what's left? Blue, violet, and indigo.
Our atmosphere loves blue. Particularly blue (475 nm). So now, when a blue photon strikes an atmospheric molecule, one of two things will happen:
(1) It will it the molecule and bounce off in a random direction. Think of it as setting a basketball down fifteen feet away, then taking a golf ball, throw it at the basketball, and try to guess which way it's going to bounce.
(2) It will be absorbed by the molecule, and instantaneously processed and spit out (re-emitted) in a completely random direction.
Awesome. But, this bounced or re-emitted photon can't go very far until it'll hit another molecule, at which point, again either (1) or (2) will happen. Then it happens again... again... again until you have billions of blue photons bouncing all over the sky, just covering it in the color blue. This is the Tyndall effect, though we all know it as Rayleigh scattering. Tyndall was a civilian scientist who discovered it first, Rayleigh was a British lord who discovered it second -- title goes to British lord. I know, it's not fair. In any case, it's because of this scattering that everyone on Earth can look up during the day, and we'll all see the exact same blue sky (our eyes might interpret the color differently, but that's a biology matter). At any rate, this is why everyone on Earth can look up during the day and see the same blue sky.
Now, I haven't forgotten about the indigo and violet photons (did you?). They're being scattered similar to the blue photons, but not as effectively because of their wavelength.
Consider that the human eye is not designed to see the indigos and violets very well, and our atmospheric molecules don't bounce and absorb indigoes and violets very well, and the overall effect is that we see the sky as blue (with violet and indigo tinting that we don't notice). As long as sunlight is hitting the atmosphere, we see blue. But when the Sun goes out at night - the blue goes away.