The First Family of Fly Tying, Al and Gretchen Beatty, did a great article on Mops in Fly Tyer 1-2 years ago. Besides the basic Weenie, they used the material in streamers, buggers, and cadis patterns.
Each nib is a piece of tightly furled chenille. So you could make your own nib out of chenille; or, as I have done, unfurl it to wrap a standard bugger body when I didn't have that color in chenille.
For whatever reason blue really works, as rich said. Matches what hatch?