Making dye mixtures to produce a certain target colour

A method for making a dye mixture to produce a target colour on a given substrate, comprising the steps of a) measuring reflectance values R T ( i ) of the target colour at a plurality of wavelengths i =1, 2 . . . n; b) measuring reflectance values R s ( i ) of the substrate s at the same wavelengths i ; c) forming a set of concentrations c j of M dyes, j=1, 2, . . . M from a database of N dyes Dn, b=1, 2 . . . N with associated constants g n , k n ; d) making dye mixtures using the M dyes in the calculated concentrations; the database having been compiled by aa) making dyeings of combinations of the dyes Dn at different concentrations; bb) measuring the reflectance values R of the dyeings at different wavelengths; cc) defining a function f(R); dd) defining a relationship between f(R) and c involving constants g and k; and ee) for each dye Dn determining constants g n , k n , such that the calculated values for f(R), c, g n , k n approximate closely the measured values.