We present a model of the colour rendering of the Cholesteric Polymer Network Liquid Crystal and a comparison with experimental results. The active medium was considered as a pile of stacked layers with continuous variable optical properties. The computation considers the optics of stratified mediums (matrix formalism) and in the complementary case analytical spectra were computed using theory of cholesterics. The spectral band and the corresponding point on the CIE (x,y) chromaticity diagram (Both colour triangle (CIE 1931) and CIELAB colorimetric space L*a*b* or L*C*h) were computed or experimentally measured, The influence of several parameters was studied such as sample thickness, pitch value, material birefringence, bandwidth broadening and modification with applied voltage.