Since I have been privelaged to have a peek into the CM's top secredt fly box, perhaps I could give you some ideas.
The older the carcass, the lighter the color of flesh. I find that beige, with a touch of light pink/orange for a bit of color, to be good. A couple strands of flash wouldn't hurt either, espcecially if the water is colored a bit.
I think CM likes to tie his on tubes but that is a personal preference. Tie in a sparse tail of light pink/orange marabou and the wrap the body with beige marabou or rabbit strips. Or you could tie the colored marabou in last at the head, your choice, but make it sparse Personally I like to use rabbit strips as it adds some weight and just use a regular hook shank with a stinger hook. Maybe have some wrapped with lead for those extra deep flows. I think the key is to make the light pink/orange barely visible.
Worked pretty well last year for me the few times I tried it.
I'm sure CM can and will elaborate.
Shane