Answer: Blue light
Step-by-step explanation:
Blue colored light will reach the depth of the sea as it is not absorbed and reaches the depth of the sea. Blue light penetrates the deepest this is the reason why clear ocean water and some other tropical water appears blue most of the time.
The particles in water affects the transmission of light inside the water. As the coastal water has more particles so they appear more brownish or greenish.
Else, the water appears blue in color.