Slide the bead onto the hook and push it toward the bend for now. It will sit set back from the eye with the hackle in front of it. Start black 70-denier thread behind the eye and lay a base all the way back to the start of the bend.
Build a small thread taper at the point where the body will end, just short of where the bead will sit. A thread taper is more solid than one built from the Krystal Flash.
Catch in one strand each of two colours of Krystal Flash with a single tight wrap and bind them back to the start of the bend. Return the thread to the front of the body position, put in a half hitch and park the thread out of the way.
Grip all four strands in spring-loaded hackle pliers and spin them into a rope. Wrap the rope forward to the front, back about halfway, then forward again so the front of the body is thick enough that the bead's hole will cover it without sliding back too far.
Catch the flash in with two turns of thread and snip the excess. Put in two whip finishes behind where the bead will sit and trim any unravelled thread tag.
Push the bead back onto the front of the body and check its position before committing: far enough back to leave room for the hackle in front, but not so far back that it closes the gap between bead and hook point. Restart the thread in front of the bead and build a thread dam so it cannot slide forward.
Take a small brown partridge feather, stroke the fibres back from the tip to make a V-notch, and catch it in by the tip right in front of the bead. Fold the tag back over, bind it down, snip the excess, and take the thread back to just behind the eye.
With hackle pliers, take about three turns of partridge (two if the feather is full enough). Catch it off and snip the excess.
Sweep the fibres back, lock them in with a few wraps, build the head, one whip finish, and a drop of head cement. Trim any stray partridge fibres.