Okay, I don't really count for this because I don't have gray hair yet, but I have dyed my hair before, and I could start showing gray any time as early graying runs in my family.

Anyway, my mom uses the stuff in a box. She tried changing her hair color once, but the dye faded too fast, so she went back to her natural hair color, which is black.

When I've dyed my hair, I've always used the store bought stuff in a box too. I had a bad highlight job in the 6th grade though, so I do not trust home highlight kits anymore at all.

Never done mine professionally, so no opinion on that, but I think the store stuff does pretty well.