I've had some gray since my late 20s (also thanks to my dad LOL). I have been using Color by Robert Craig for about 15 years and love it! Hair Color and Hair Care by Robert Craig Salon Products, Ltd.
It is very gentle as it does not contain alcohol/ammonia/peroxide, it is deposit-only and won't lift color. I have medium to dark brown hair and use Golden Chestnut (or sometimes Light Chestnut for the roots only).
As with any color, you do need to choose a color about 2-3 shades lighter than you want to end up with, as most hair colors end up darker than they box shows.
In using the lighter shade, it also turns my grays into natural highlights.
LMK if you have questions or want help choosing a shade if you want to try it. I've been named the resident RC Guru as I've helped lots of curlies choose colors and use RC successfully.