What is the best hair color out there that will total cover gray and last longer then 2 weeks?

I would talk to a stylist. Keep in mind your natural hair color, texture etc. You would probably be better off getting a color that's not a permanent. My grandmother does this, but it leaves her hair dry and fuzzy, which she hates more than the gray. She was a natural red head, but now she opts for the dirty blond as she finds it blends better with the gray, making it less noticeable. Don't know that any of this will help, but good luck.What is the best hair color out there that will total cover gray and last longer then 2 weeks?
red my mom has not colored it for four weeks and she old 40s