What I am saying is that natural black hackle tends to have much softer fibers than natural white hackle. The dying has no effect on the stiffness of the fibers. It is a function of the bird genetics. That is why the dyed black (from white stock) has stiffer fibers. This is not only my observation but the word from the man himself, Tom Whiting. We had this specific conversation at one of the FFF conclaves a couple of years ago.

Along these same lines of bird genetics, brown hackle always tends to have stiffer fibers than grizzly hackle.

I have never noted any adverse effects caused by dying.