In general, the ocean appears blue because water absorbs red light more efficiently than other colors of light. This means that the blue light is reflected back to our eyes, making the ocean appear blue. However, the ocean can also appear green or turquoise in shallow areas where the sunlight can reach the bottom and reflect off of the sand or other objects.
The color of the ocean can also be affected by the presence of particles in the water. For example, the ocean can appear brown or murky near the coast due to the presence of sediment or pollution. The ocean can also appear black in deep water where the sunlight cannot reach.