Why do men have grey hair on their penis?

Not all men have grey hair on their penis. I've never even heard of that.

If a man has had a very hairy penis, I mean like the hairs around it extend most of the way to the top like mine, as I have got older the hair has got a bit grey. I notice where I was hairiest on my body, head hair, shoulder hair, chest hair was very thick, all these places started to get grey in my 50's, my arms and legs, slightly less hairy are still brown, the colour I was when the hairs started when I was 13 or 14. I am proud to say that I have never cut 1 hair off my body, I am 66 to be exact, only my head hair has been cut, and that is by my barber.