"Lots of hairdressers are telling clients not to use box dye, but I think it's inevitable," Howard said. If you've exhausted all other options and just cannot resist picking up some box dye, then reach for demipermanent. Howard recommends demipermanent (which differs from semi, as it lasts slightly longer) to blend any grey hairs and roots. Schaudt also recommends a "demipermanent rinse, as it's the most noninvasive pigment."
Howard also says not to get too disheartened if your hair doesn't turn out exactly as you wished. With semi and demipermanent dye, you can't do too much damage. Just know that your colourist will be waiting to fix any mishaps and at-home mistakes as soon as the time is right. Although, keep in mind that fixing at-home hair-colour mishaps can sometimes cost you more than if you left your hair be.