Any LED can be used, but mine used the light the fiber-optic (FO) strands came with (hence the hair clip)

I poked the FO strands through the faux fur fabric backing, secured it with low-temperature hot glue (higher temps can melt it and cause the light to scatter, leading to a dimmer or nonexistent fiber-optic effect)
After securing enough strands, I collected them together and added a little hot glue to keep them together before putting them back into the sheath that connects to the LED. I imagine this could be replicated by using a tape (probably best to be opaque, like an electrical tape...?) to connect the LED of your desired color to the strands