The inhabitants of great depths are usually black and red
Most people have so far wondered what colors are present in the depths of the sea as they walk the green grass in red sneakers and watch the blue sky and the orange sun. The inhabitants of great depths are most often black and red. The reason is simple. At a depth of 50 meters, blue is the only visible color. This means that the red inhabitants (Australian starfish, New Zealand bodianus fish, Mexican red sponge, Thai prickly star) become invisible and thus protected from the enemy.
In the water, the yellow color is visible up to 15 meters deep. Divers-photographers use a flash to capture photos of yellow-colored marine life (for example, a butterfly fish from the Red Sea, a sea lily from Papua New Guinea, a ball fish from the Galapagos, or a yellow box fish from the Solomon Islands).
The black and white world in the lives of people but also of all other living beings would be sad and ugly without a doubt. We are surrounded by colors that make the environment happier, more pleasant and cheerful, but the colors affect the health and mood of people and other living beings. Science says that white sunlight is a set of many rays of different wavelengths and the colors depend on the length of those rays. The human eye (actually the brain) perceives and reads only electromagnetic waves of length 380 to 780 nm (nanometer), ie the part between red that emits waves of 620 to 760 nm and purple that emits waves from 390 to 450 nm. The transitions between colors are gradual. The human eye can distinguish about 160 shades of color across the entire visible color spectrum. That’s enough for people to see the world around them as an endless colorful world.
A mixture of red and blue or purple is a very rare color in the marine universe. Among the few species of this color are ivory sponges and sausages from the Solomon Islands (which live in symbiosis with the fish Amphiprion perideraion), corals from Micronesia and corals from Australia (which have a lovely color because they eat purple algae).
Chlorophyll is a natural pigment in the cells of plants or organisms that perform photosynthesis. In seawater the green color is at the bottom where there is plenty of vegetation. Due to the star coral, the bottom around the island of Similan (Thailand) looks like a green meadow in the spring inhabited by green inhabitants.
Coral reefs are the habitat of many brightly colored species. The very conspicuous orange and the mixture of yellow and red in the marine world are a sign that these living beings are armed with poison. Some orange marine inhabitants (such as the Australian Black Sea) can change color as needed and thus become red.
Most fish that live on the surface of the water have a blue-green back and dorsal fin that allows good camouflage and salvation from birds of prey. Among the most blue marine inhabitants are the Australian fish Napoleon, which can grow up to 2 and a half meters, the Cuban fish Chelinus undulatus, the angel fish from the Red Sea and the blue starfish from Australia.
Professional divers, underwater cameramen and connoisseurs of the sea depths know that human notions of the richness of the sea depths often do not correspond to reality (acquired mainly on the basis of brightly colored inhabitants of tropical and warm colors). It depends on the amount of total light. The colors gradually disappear in the water going towards the depth. Red disappears at a depth of 5 meters, orange disappears at 25 meters. Blue is the most persistent and can be seen at about 100 meters depth. After that, darkness ensues in which the inhabitants of the sea depths can only be photographed with a flash.

https://www.livescience.com/deep-sea-anglerfish-washes-ashore.html