Hi bn,
With fish alot is still not known but the fish that live closer to reefs tend to be able to see more colours, those at depth tend to have more focus visually to pick up light and silhouettes of prey above but less colour ranges. In the ocean we haven't found any really pattern for fish and vision and we are still looking, with freshwater fish its just a chaotic mess. Almost nothing has been down on fish that live on the bottom like flathead. My focus at the moment is to start by determining what colours flathead can see (if any) and how the eyes of Flatheads are structured. I also what to look at how it changes between species.
Hope that gives you some idea,
Anthony