No matter the type or brand, the black stuff is usually carbon. That's what they use as a conductor as opposed to a metallic core. It will conduct electricity, if you get good contact between it and the screw in the CDI. Resistance wire has all kinds of different construction. Some have fiberglass, some cotton, some polymars. The key to using it on our bikes is the very center core, whatever color it is. That's where the conductive material is and where you want the screw in the CDI to make contact.
The wire, if correctly sized, about 7mm, should be self centering into the CDI's socket. To assure that, the end of the wire must be cut square and flat. I'd use a very sharp razor blade.
Tom