The blue color of seawater is due to the reflection and absorption between light and seawater. Sunlight is composed of seven colors: red, orange, yellow, green, blue, indigo, and violet. The wavelengths of these seven colors of light are different. From red light to purple light, the wavelength gradually becomes shorter, and the long wave has the greatest penetrating ability. It is strong and most easily absorbed by water molecules. Short wave has weak penetrating ability and is prone to reflection and scattering. What we see is the color of the remaining blue and purple light after being scattered by sea water. Since the human eye is not as sensitive to purple as blue, the ocean we see appears azure.