Home of Rhett & Link fans - the Mythical Beasts!
His mom or dad (either, I forget) got grey hair in their early years and link gets it from them. He died his hair back to his normal colour to cover up the grey, but now he said that he is letting it go grey and not dying it anymore.
He didn't dye it gray; it's naturally going gray. He talked about his decision to stop dyeing it black in this Ear Biscuits episode (around 4:40): https://youtu.be/BaVnd2PtxJg