The wavelengths of light that WE see as colorful are filtered out as water depth increases, the shorter wavelengths penetrating deepest. But I know of no study that shows which wavelengts of light fish are responding to, which wavelengths they associate with which colors, or if they see in color at all. For all we know, their visible spectrum might include X rays and gamma rays, and they might be seeing colors that we can't even imagine.
