I don't ever recall it being jet black. I would say it was more of a dark brown with a reddish tone. Some old magazine articles that I have from 1974 and 1975 even describe him that way. I definitely noticed the color change that you are talking about though. It got more red. He also started getting some sort of body wave in his hair in the late 80's or early 90's. He was a man of many hairstyles. It is too bad that most of his best moments in tennis happened when he had that Prince Valiant hairstyle. It is how he will always be remembered.