This is an interesting post suggesting that there is a pathway to reverse graying.
Repigmentation And New Growth Of Hairs After Anti–interleukin-17 Therapy With Secukinumab [Study in comments] from tressless
2018-06-14 07:06:312018-06-19 08:59:45Reversal of Graying with Anti–interleukin-17 Therapy With Secukinumab (from Reddit)