it´s dark in fact like space itself <br />
but because our planet has an atmosfere , when suns rays come down on earth, the sky gets blue<br />
so , night is like the "real" sky
"Blue is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.As the Sun gets lower in the sky, its light is passing through more of the atmosphere to reach you. Even more of the blue light is scattered, allowing the reds and yellows to pass straight through to your eyes." forgot to mention this too http://spaceplace.nasa.gov/blue-sky/en/ took it from here it´s an easy explanation
2/3 of the planet is covered with oceans and seas which is blue. So light reflects from it and makes the sky blue as well.
Well if that's the case, then during storms and cloudy weather when the sky turns black, the water should also become black.. i guess that's not what happens..