Investigation of ink formulation options with the purpose to obtain color-gamut-optimal set of Cyan Magenta and Yellow CMY inks is reported. Implementation of the thickness dependent Kubelka-Munk model on multiple ink layers having different and well-defined thicknesses, provides characteristic absorption and scattering (K,S) spectra of the ink ingredients. These data enable accurate computation of the reflectance spectrum and thus theL*a*b* color coordinates for any given ink thickness or substrate. Pigment materials investigated are quinacridone as magenta, copper-phthalocyanine as cyan, and arylide yellow. Scaling the peak of the absorption band to the number of molecules per unit area for the specific pigments studied in this article provides the molar extinction coefficients,1.21 x 10(4),4.7 x 10(4), and3.3 x 10(4)cm(2)/millimole respectively, regardless of the different ink formulations used, in accord with Avogadro's principle. Having a set of three pairs ofK,Sspectra is used to compute the color gamut of any CMY color combination in theL*a*b* space as a function of ink layer thickness and formulation. Using an iterative algorithm, a color-gamut-optimal set of CMY inks is obtained.