Tungsten bead Gold bead (1, sized to hook (5/64" for #14))
Pheasant tail fibers Natural brown pheasant tail fibers (3-4 for the tail)
Thin Skin or turkey tail Mottled brown thin skin (1 slip for the back/wingcase)
Copper wire Copper wire (small, for the rib)
Superfine or nymph dubbing Pale golden yellow superfine or nymph dubbing (a pinch)
Hungarian partridge Brown hen hackle (1 feather for the legs)
How to tie it
Slide the gold bead to the eye, small hole first, and start yellow thread behind it. Cover the rear two-thirds of the shank with a smooth thread base so nothing slips.
Bind a sparse tail of 3-4 pheasant tail fibers at the bend, tips splaying just past one hook gap, no longer. A yellow sally nymph is a slim bug, so keep it thin.
At the tail tie-in, catch the copper wire and a slip of brown Thin Skin, shiny side down, and leave both hanging off the back. The dark back over a pale belly is the whole point of this fly.
Dub a slim, tapered pale-yellow body forward to the 70% mark, building a slightly heavier thorax up near the bead. Use half the dubbing you think.
Pull the brown Thin Skin taut over the top to form the back, bind it at the thorax, and counter-wrap the copper rib forward in 5-6 even turns to lock the back and segment the body.
Fold a partridge feather and take 1-2 turns as a soft collar behind the bead, then sweep the fibers back and down to a length of one hook gap for legs.
Build a small yellow thread collar, whip finish behind the bead, and add a drop of cement.