Answer:
Blue
Step-by-step explanation:
Red and orange light waves have less energy, so they are absorbed near the ocean surface. Blue light penetrates much farther, so blue objects are more visible in the deep. Red light is the first to be blocked. This is the reason that if you bleed after a depth of 30 meters or so in Indian ocean ,your blood will appear black not red. The exact measurements differs from seas to seas because their optical densities may be different.
If you look at the internet for an explanation ,you will find many. There are many theories whether it’s Rayleigh scattering, or because blue light has the smallest wavelength and the highest frequency so it has the most energy so it goes further. There are many explanations but it will take time to conclude to a single explanation. The observation is the same
Blue light (the color of light that has the highest frequency) is the one that penetrates the deepest.