PRO TIP: "The longer the formula is on, the lighter hair becomes. Brown hair only needs about three minutes, or it gets too brassy," says colorist Kyle White of N.Y.C.'s Oscar Blandi Salon.
PRO TIP: If your brown hair is dark to begin with, don't assume black is the only way to go deeper. Unless you're deliberately going for the Morticia effect, "never, ever dye it black," White says. "Black dye is too dense and toneless. Instead, choose one of the darkest brunet kits available."
PRO TIP: Picking a predominantly red kit can overpower blond hair. Instead, Kyle White says to use "a warm brown, almost a honey color, to add just a hint of red."
PRO TIP: Keep red or auburn hair vibrant with cherry Kool-Aid, White says (use grape to neutralize brassiness in bruet shades that have been lightened). Make a pitcher, boil, let cool, and massage into your hair. Allow it to sit for 15 minutes under a shower cap and rinse.