Black is negative, but I see your point.
>>Black is negative...
Understood. I guess the person who originally sent the email was speaking of the green felt washer that often sits on the negative terminal of a car battery. But the sentiment is the same! :)
Actually, I had always wished that Ben Franklin had gone the other way when he chose which side to call negative and which side to call positive. I think electon theory would be simpler to understand if it was thought of as a positive pressure of electrons. Maybe the biggest mistake of his career.