In this book the complex impact of colour action on the organism is discussed. It is shown that the perception of colour depends on the action of irritants on other sensor systems and, vice versa, the action of colour may exert exciting or inhibiting influence on the perception of sounds or smells. The facts of mutual influence of the sensor systems force us to consider not only a single observation but the entire experience as a continuous flow of sensations which is formulated as the empirical monism principle. This book proposes the solutions of these problems from the point of view of perception's activity and continuity.