There are two things people mean by covering grey, and they end up looking very different. Full coverage puts a single tone over everything. Blending lowers the contrast so the grey reads as a highlight.

Coverage grows out with a hard line at the root, which means committing to a schedule for as long as you keep doing it. Blending grows out invisibly, so if you stop, nothing announces it.

Nine out of ten people who ask us about grey want blending and do not know the word for it. If you are unsure, start there — you can always go further, but you cannot un-dye.