The way we see water, and the way fish see water is drastically different,as we all know. Even on a cloudy day, in dirty water... when the fish look 'up' they see a well lit background. You dont need much ambient light to make the above water look very well lit. And with such a bright(relatively speaking) background, it makes sense black shows up best. In murky water, the sediment breaks up that light, and it becomes a much more 'even' tone.

We got some underwater video on the Situk this fall, and over the season the water started to really color up. We went from just about anything working in clear water, to black, or sometimes purples, and blues. But the name of the game was, DARK for muddy water coho. I think having that, big black profile, is actually all the contrast you need. Its a perfect contrast color, to how fish see water in muddy situations.

Hard to explain without seeing it, but there has got to be a youtube clip of some fly tests in all sorts of water conditions, that touch on color...