Hi Iain
I have been using a thread very similar to Sheer by Gordon Griffiths, loads of great colours, splits well and you can finish off parachute flies under the parachute hackle without causing the hackle fibres to flare upwards.
Send me a PM and I will see if I have a spare spool (I will have transferred the thread onto a sewing machine spool though).
Works great with a small Matarelli bobbin holder.
Kev.