It should be green. But it sometimes can depend what brand you have, tell me what brand you have and I can help you, but all around, it's usually black and connects into the correct speaker plug in the back of the computer.
There is no specific cable color of a computer speaker cable. The connector on the sound card is green on newer card and the same on headphone or speaker cable "connector" (the thing at the end of the cable). The cable itself is likely black. What exactly is the problem you are having?
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