Salt and pepper from completely white hair

[Nowayhozay]

My friend in his early fifties has completely white hair, he went grey early which didn't bother him but now feels that being completely white is aging him.

Has anyone any suggestions for something like a shampoo that would create that salt and pepper look ?

A shampoo simply can’t do this because salt and pepper is a mixture of dark and white. There’s nothing that can colour some hairs but not others, apart from highlights and lowlights