The eye is considered as the most important human sensory organ. Its important part is the retina, which converts light to neural impulses by several millions of sensor cells: rods and cones. To understand this process, modelling by computer simulation is required. The well-known phenomenon of afterimages is examined in this paper. When a fast color change on screen is performed, a color after image appears temporarily. This afterimage may result in a more intensive color perception. A model was established to characterize the color perception intensity and duration depending on color changes.