Abstract: An array of hair dye products formulated to provide the same hair color to users with different hair colors or a different variety of colors of users with the same hair color. The array includes at least two hair dye products. The hair dye products each include a hair dye composition contained in a package. A first hair dye product in the array includes a photochromic dye that provides a color change to a first hair color, and a second hair dye product in the array includes the same photochromic dye that provides the same color change to a second, different color of hair. The array may also include two or more hair dye products that contain different ratios of photochromic dye(s) to provide users with different hair colors the same or different tunable hair colors.

Abstract: A tunable hair dye composition that includes a photochromic dye, a cosmetically acceptable solvent and, optionally, a carrier. When activated with a suitable activating electromagnetic radiation, the photochromic dye molecule changes color, thereby imparting a temporary color change to the composition and hair to which it is applied. When deactivated, the photochromic dye is generally colorless. The color imparted by the photochromic dye can be tuned by adjusting the wavelength and/or fluence of the activating and/or deactivating electromagnetic radiation. Thus, a wide variety of different hair colors can be obtained from a single hair dye composition containing specific combinations of photochromic dyes.