Mike, copper oxides are actually dark red to dark brown(e.g. an old penny). The green stuff apparently is a result of the polyvinyl chloride in the jacket breaking down and releasing chlorine gas, which reacted with the copper to form copper chlorides, which are green. Okay, so regardless of the chemistry involved it may still look crummy, but it shouldn't appreciably affect power transmission if you keep the stripped ends clean where they make contact with the terminals.

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Enjoy the music, not the equipment.