Root “tapping” is when a tiny amount of your natural color is applied just on a small amount of hair at the root, in the same manner root smudge is done but
Just be sure you let each layer dry before applying another one so as avoid any bubbles or smudges from forming when working with them in layers- start by brushing up against areas where there may already show some cracks or chips for example near doorways since these spots tend hang around...