A method for treating hair, in which using as a boundary a depth X % in a range of 5% to 80% from the surface of hair toward the center along the long diameter axis extending through the center of the cross-section of hair, hair is divided into an A layer (a portion of a continuous color from the surface of hair to the depth X %) and a B layer (a portion including the center and having a continuous color different from the A layer, in which the depth from the surface of hair exceeds X %) and at least one value of Δ；F*, Δ；h and Δ；C* between the color of the A layer and the color of the B layer is adjusted to 3 or more to change the hue and the color tone of hair appearance depending on viewing angle of the hair. A method for dyeing hair, having Step (I) of dyeing hair with a two-part permanent hair dye agent, and Step (II) of dyeing hair with a hair dye agent comprising a dye selected from (A-1) to (A-8).
