No one knows for sure. There are several theories as to why the ocean is usually blue. Some scientists believe that when sunlight hits seawater, part of the white light is absorbed and part is reflected. Seawater does not absorb blue light, so the blue light is reflected outwards. Some scientists believe that suspended matter in the sea is responsible for its blue color.
Wind is the most common cause of surface waves.
The longer the distance a wind blows, the stronger it is, and the bigger the waves. As wind blows over the ocean, it tries to pick up some of the water. Because the surface of the water can not move, it rises. Gravity pulls the wave pack down into the ocean. However, the water now has momentum.