In real life when you go below a certain depth in the ocean colors start to change drastically because of things like light refraction. In Subnautica it's heavily implied that planet 4546B is comparable to the oceans of Earth however, it is an alien ocean. Still, I have noticed that, depending on where you are and, what the time of day is there does seem to be a color change to certain things. Mostly it seems like anything not glowing simply gets very drab. Though, it does seem to be at a much deeper depth than in real life.
In our oceans, depending on how clear the water is, it only takes about 15 to 20 feet for things to start loosing their colors. Just for reference one meter is about 3.2 feet. So going down 48 meters is roughly 155 feet or so. By the end of the video I dive down over 200 meters. That's over 640 feet below the surface.