So say your in water. Water is really dense, and based on how deep you go and how dense the water gets the light should be blocked more than just being at the surface. This could work even for other planets like tydos if you fall into the planet, it will slowly get darker as you fall. Well, darker than it normally gets in game.
Also, maybe a setting to switch off the weird distortions of the water itself. Or if we use a camera or something it would just be like a normal view, just underwater.
Oh, idk if this sounds greedy or anything, but Here is the actual suggestion so if you want this to be maybe considered.
@zeropol it only applies a filter to the image, it's not even a translucid material, so it looks the same no matter the distance of the object you look at.