I have to ask...If red suposible turns to grey around the 20' depth, is it the shade of grey their attracted to down at 40'? I've had sucess with the color grey and black at depth, and wondered why more tackle companies don't carry these colors.
I think fish are adept at perceiving gray scale. Salmon's eyes are much like a humans with the exception of using UV to hunt plankton in the upper water column. So . . . yes I think they no where on the gray scale red lies when all colors turn gray. I think red also has a good contrast against the underwater background. We've been experimenting with colors for next years crop vs. colors for the spawing class. At 35 to 40 feet next years class is hitting green at a rate of 4 to 1 over red. Just the opposite for the spawning class and the males are not touching the green at all while the try to rip the red apart!
Now for gray. I watched a show that was a color test for steelhead. They would move steelhead through a channel tube and see which colors were hit the most. The big surprise was the color of a lead splitshot was the number one color in test after test!