I have salt & pepper hair in the crown darkest brown just below that and salt and pepper in my ponytail and the front. To make it all shine, I use a white vinegar rinse.
Worried about what color you will have? I don't have a choice. If I cut it shorter, looks like a bad dye job. Better to leave it long and work with it. It is a challenge but a good hairdresser can make it work beautifully.