A method for determining and producing, in a computer-assisted manner, a hair dye for dyeing hair in a desired hair color, comprising: • determining a value or values for at least one initial condition parameter which describes an initial condition of the hair to be dyed; • determining a plurality of hair colors which can be achieved by dyeing using an available hair dye, based on ∘ a relationship, determined on the basis of hair color data for a plurality of dyeing processes, between a plurality of dyeing prerequisite parameters and achieved hair colors, wherein the plurality of dyeing prerequisite parameters influences the particular dyeing process, and the achieved hair colors are achieved by means of the particular dyeing process, and ∘ the value or values for the at least one initial condition parameter; • selecting the desired hair color from the plurality of hair colors which can be achieved by dyeing using an available hair dye; • determining the hair dye for dyeing hair in the desired hair color based on the desired hair color and the determined relationship between the dyeing prerequisite parameters and the achieved hair colors, wherein the at least one initial condition parameter has a basic hair color, wherein the plurality of dyeing prerequisite parameters comprises a plurality of concentrations of dye precursors and at least one of the initial condition parameters; and wherein determining the hair dye for dyeing hair in the desired hair color comprises: • determining a plurality of color distances, wherein each color distance from the plurality of color distances is a color distance between the desired hair color and a hair color, calculated on the basis of the relationship, for one of a plurality of hair dyes; • determining a minimum color distance from the plurality of color distances; and determining the hair dye associated with the minimum color distance as the hair dye for dyeing hair in the desired hair color, wherein the determination of the hair dye for dyeing hair in the desired hair color comprises: • determining, proceeding from the desired hair color and using the determined relationship between the plurality of dyeing prerequisite parameters and the achieved hair colors, a combination of dye precursor concentrations which, according to the relationship, results in the desired hair color when dyeing the hair, wherein the combination of dye precursor concentrations is part of the hair dye for dyeing hair in the desired hair color, • producing the determined hair dye for dyeing hair in the desired hair color. • determining a value or values for at least one initial condition parameter which describes an initial condition of the hair to be dyed; • determining a plurality of hair colors which can be achieved by dyeing using an available hair dye, based on ∘ a relationship, determined on the basis of hair color data for a plurality of dyeing processes, between a plurality of dyeing prerequisite parameters and achieved hair colors, wherein the plurality of dyeing prerequisite parameters influences the particular dyeing process, and the achieved hair colors are achieved by means of the particular dyeing process, and ∘ the value or values for the at least one initial condition parameter; ∘ a relationship, determined on the basis of hair color data for a plurality of dyeing processes, between a plurality of dyeing prerequisite parameters and achieved hair colors, wherein the plurality of dyeing prerequisite parameters influences the particular dyeing process, and the achieved hair colors are achieved by means of the particular dyeing process, and ∘ the value or values for the at least one initial condition parameter; • selecting the desired hair color from the plurality of hair colors which can be achieved by dyeing using an available hair dye; • determining the hair dye for dyeing hair in the desired hair color based on the desired hair color and the determined relationship between the dyeing prerequisite parameters and the achieved hair colors, • determining a plurality of color distances, wherein each color distance from the plurality of color distances is a color distance between the desired hair color and a hair color, calculated on the basis of the relationship, for one of a plurality of hair dyes; • determining a minimum color distance from the plurality of color distances; and determining the hair dye associated with the minimum color distance as the hair dye for dyeing hair in the desired hair color, wherein the determination of the hair dye for dyeing hair in the desired hair color comprises: • determining, proceeding from the desired hair color and using the determined relationship between the plurality of dyeing prerequisite parameters and the achieved hair colors, a combination of dye precursor concentrations which, according to the relationship, results in the desired hair color when dyeing the hair, wherein the combination of dye precursor concentrations is part of the hair dye for dyeing hair in the desired hair color, • producing the determined hair dye for dyeing hair in the desired hair color.