Touch-Up

Place the two pigments into a large bowl (or a large-bowl-sized hole, dip, etc) and fill 3/4 of the way with warm water.

Stand in front of the bowl. The water and the pigments will swirl for a couple seconds before making the dye. If the pigments are the same, the dye will be a solid color. If the pigments are different, the dye will appear like tie-dye.

While standing in front of the bowl of dye, run your fingers through your hair. The dye will swirl upwards into the air a short distance before evaporating.

Roll a d20 with no modifiers. This will determine the outcome of the spell.

On a 1, your hair is not changed at all.

On a 20, the spell malfunctions and dyes your hair the invert of your intended color.

Upon rolling anywhere from 2-19, your hair will be dyed as you envisioned, so long as the pigments are close enough to the right color(s).

Roll a d20 with Advantage. This number will determine how long in days the dye will last until your roots start to become visible again.