I don't know what materials are used. But if you are talking about the alternating bands of color(light and dark) on the fly behind the abdomen, it looks
like it could be a Banded Weave. It is discussed in The Fly Tier's Benchside Reference to Techniques and Dressing Styles in Chapter 10:
Bodies Section 12 Woven Bodies Method #111.
Thanks for the advice, I'll give the benchside reference a look for sure.
Hope it's not too time consuming to do a weave.