I would like to extend this question (unanswered)
I read here that,
“The Jews and the Christians do not dye their hair, so be different from them.” (Narrated by al-Bukhaari, 3275; Muslim, 2103).
إِنَّ الْيَهُودَ وَالنَّصَارَى لاَ يَصْبُغُونَ، فَخَالِفُوهُمْ
So is keeping grey/white hair not permissible in Islam ? I couldn't find any more references.