Thread Brown and yellow 140 denier brown, 70 denier yellow
Materials
Tail/shuck Brown permanent marker (McFlylon+)
Body Yellow mcflylon (Nature's Spirit turkey biot quill)
Wing 1 Bleached material (Select cow elk)
Thorax Orange permanent marker (SLF Bug Dub, Hare & SLF)
Wing 2 Yellow mcflylon (CDC feather tips)
Head Yellow mcflylon (CDC feather)
How to tie it
Start the brown UTC 140 at the 70% mark and tie in a sparse brown McFlylon shuck at the bend about a shank long, trimmed to a wispy trailing tuft. The nymphal skin the insect is climbing out of.
Tie in a yellow turkey biot at the bend and wind it forward to the 60% mark with the notched edge trailing so each wrap throws a crisp ridge. Biot gives the hard, tightly segmented abdomen of a sulphur or PMD better than dubbing can.
Switch to the yellow UTC 70 for the front of the fly, then stack a small bunch of bleached cow elk and tie it in at the 65% mark as the first wing, tips angled back over the body. Bleached elk is both buoyant and highly visible from above.
Dub a short thorax of orange SLF Bug Dub around the elk wing base. The orange is the hot spot: on an emerger a warm thorax reads as the insect's swollen, splitting wing case.
Tie in yellow CDC feather tips as a second wing over the elk, standing them up as a shuttlecock. The CDC keeps the front of the fly in the film while the biot abdomen hangs below.
Finish with a yellow CDC feather wound or folded as a head, whip finish small, and trim the elk wing to length. Fish it dead drift in the film during a sulphur or PMD hatch, especially when fish are refusing the fully-emerged duns.