In my split case PMD thread I mentioned the ISO being another good split case nymph...
here's my version of the ISO and it works well here for me.
Thread 6/0 black
Tail - pheasant flank
flashback - purple metalic flashaboo
Rib - ultra fine black wire
Body - waspi antron ;dark stone
Thorax - waspi antron ;dark stone
wing case - black goose biot & purple foam
Legs - Golden Pheasant shoulder
The Golden Pheasant shoulder feather is a really cool blue'ish purple and with the purple flashaboo flashback and foam split case its a pretty good color mix. I tie it also in a green and the pheasant flank tail looks better with that but the fish don't seem to mind and this purple attracted better with both color combo's fished in the same cast of flies.
Edit: forgot to mention how I fish it....
I tie two on about 16" apart and quarter cast...dead drift with lesinring lift and then strip back in 6" strips. These little guys are swimmers and its the stripped retrieve that best immitates the nymph. I can cover alot of water and its a fast stripping retrieve with some dead drift pauses thrown in. Deadly this time of year around here.