Hi ,
You’ll want to use a directional light in your scene along with adjusting some values in the post process to get the right look.
In the directional light you can adjust the values for the light to be more of a darker color like blue/purple. You’ll also want to use a skysphere to get a good night sky.
Here is a scene I set up in less than 5 minutes using the ocean plane, water material, and a sky sphere from the Features Tour 2014 content that was recently released on the Learn Tab in the launcher.
I hope this helps!