A system for determining hair color treatment, including a processor. The processor is configured for: receiving as input an initial spectrum of a sample of hair, the initial spectrum having a wavelength range； calculating a new spectrum of the hair due to a hypothetical hair color treatment as a direct function of the initial spectrum； and outputting data to a device, the data being based upon the step of calculating. The system also includes a spectrum analyzer configured for producing the initial spectrum and a display device configured for displaying a color and hair color treatment instructions based on the data. An alternate embodiment of the invention includes a color mixing device configured for dispensing a hair color treatment based on the data.
