Modern theory of color vision holds that there are three kinds of color sensitive pyramidal cells on the human retina, which are sensitive to red, green and blue colors respectively. The process of color vision can be divided into two stages. In the first stage, the three kinds of pyramidal cells on the retina selectively absorb radiation at different wavelengths of the light spectrum. At the same time, each substance can produce white and black reactions which white reactions will be under strong light and black reaction will be without external stimulation; In the second stage, during the transmission of nerve excitation from the vertebral receptor to the visual center, these three reactions are recombined to form three pairs of antagonistic nerve reactions, namely red or green, yellow or blue, white or black, and finally produce various colors in the brain nerve center.
Each color in nature can be selected. The red, green and blue primary colors that can stimulate the three receptor cells in human eyes are mixed in an appropriate proportion. Therefore, a new concept called tristimulus value is introduced, that is, the three meta stimuli that match the color to be measured in a given tristimulus system are represented by X, y and Z respectively, After extensive color experiments on many human eyes with normal color perception (i.e. standard observers), the color matching functions of the relative number of vertebral body stimuli caused by each visible wavelength (400-700nm) were measured. These functions were combined and drawn into curves to form the spectral tristimulus value curve of our standard observers (see Fig. 1-1).