There is only one product out there (that I am aware of that) you can apply to your hair and it will turn the grey hairs back to their natural color. It’s called GreyBan. It’s not a dye. GrayBan works with the natural protein in hair to create melanin that gradually brings back your hair color.
I have not used this myself, but it gets good reviews from most people who have used it. They say you have to stick with it and not give up and after three weeks, you’ll have your natural hair color back. It’s worth a try.