This is what I think it is because I use it for many of my flies and it gives off the blueish halo when in the water. I use a material called SAAP Hi-Vis in white. They make other colors. I purchased mine at Jimmy's All Season Angler in Idaho Falls, ID.
Here is one of the flies I use it on:
Improved Shop Vac (Original Shop Vac fly was developed by Craig Matthews at Blue Ribbon Flies in West yellowstone. The 'improved' part of my fly is to add a peacock collar, use a copper bead and rib with chartreuse wire):
Tight Lines,
Kelly.
"There will be days when the fishing is better than one's most optimistic forecast, others when it is far worse. Either is a gain over just staying home."
Roderick Haig-Brown, "Fisherman's Spring"