The new story framework features two fish; one living near the surface of the ocean and one living within a ravine in the ocean depths. The two of them are driven towards the "centre", the ocean floor. We considered the idea that both the bottom of the ravine and the waters that meet the surface are both "unknown" zones areas, they represent somewhere mysterious, possibly scary while the ocean floor is the point of knowing; it is familiar and inviting.
One idea we had considered for style is that the deeper you go, the less saturated the world becomes. The depths of the ravine would be black and white while near the surface would be very bright colours. I made some very quick tests below for this to test how colour could be used within the project.
Picture two uses a modified gradient. Here there is a banding of the saturation levels going on, with the mouth of the ravine being the threshold between colour and monotone. While the difference between the open ocean and seafloor saturation levels is also a little more tightened.
Picture three uses the same banding as picture two, but there is also a brightness filter that sharpens the colour intensity of the ravine and the ocean surface with a more muted brightness around the seabed. The idea being that the brightness adds a certain "unreality" to the area they are in. The fish that live in these areas are also more familiar with their environments, so brightness could also suggest familiarity. The ravine may be dark, pitch-black even, but to the fish that lives down there it is familiar. To the fish there's nothing uncomfortable with simply being there and the environment could reflect that.