My opinion on the black lines on spin-n-glos, and their white or metallic wings, is that they provide contrast.

A pink winged bobber with pink wings would look a lot like a pink corky until you were very close to it, while one with white wings has very visible movement and action from much farther away. The same thing would apply to the black lines on the bobbers.

Fish on...

Todd
Wild Steelhead Coalition