Kubelka-Munk  equations:

•         The mathematical basis for all color matching software is the Kubelka-Munk series of equations. These equations state that for opaque samples such as textile materials, the ratio of total light absorbed and scattered by a mixture of dyes is equal to the sum of the ratios of light absorbed and scattered by the dyes measured separately. Where absorption is defined as "K" and scattering is defined as "S", Kubelka-Munk states that _:

             (K/S) mixture = (K/S) dye 1 + (K/S) dye 2 + (K/S) dye 3 + ...

K/S is not a readily measurable quantity, but it can be calculated from the reflectance of a sample -- "R" -- by the Kubelka-Munk equation that states

                                 K/S= (1-R)²/2R

K/S  value is proportional to dye  concentration in the substrate. Means dark shade will have higher K/S and Light shade will have lower K/S value.

Now-a-days computer colour matching is used to determine the K/S value.