Induction refers to the change of the color appearance of a light caused by the presence of neighboring lights. There are two major types of induction: color contrast, which occurs when the color appearance of a light shifts away from the color of the neighboring lights; and color assimilation, which occurs when the color appearance of a light shifts toward the color of the neighboring lights.Previous studies reported that spatial properties are the main factor determining the transition from assimilation to contrast. With high spatial frequency stimuli, assimilation occurs. With low spatial frequency stimuli contrast occurs. With intermediate spatial frequencies, variable effects are seen. The purpose of this study is to investigate the mechanisms of the induction. To achieve this goal we measured the induction effects for different stimulus spatial frequencies (0.8, 4.0, 6.0, and 9.0 cpd) to determine the transitional spatial frequency between assimilation and contrast. The use of a cone excitation space allows analysis of the spatial frequency effects on SWS and LWS/MWS cones chromatic pathways separately. A spread light model was developed to see whether optical factors might account for all or part of the assimilation effect.