Is the ocean really blue?

  A glass of ocean water looks clear and colorless, like a glass of drinking water. But if you stand on the deck of a ship and look about you, the water is sometimes blue and sometimes green. What makes the difference? Sunlight makes the difference. Sunlight has no particular color itself, but it is a combination of all the colors of the rainbow. When sunlight falls on the ocean where the water is deep and clear, only the blue color is reflected back to your eyes.
  What has happened when ocean water looks green? Billions of tiny plants and animals have grown in the water. They reflect green light. And so the sea looks green.