To demonstrate Subjective Color Illusion.
Colors that appear when rapidly alternating patterns of black and white are observed is known as Subjective Color Illusion. To demonstrate this phenomenon, draw with a black ink pen on a white circular cardboard disc, the circle patterns as shown in the figure. Mount it by pushing a pin through the centre and spin the disc rapidly. When the disc is spinning ,concentric circles of different colors will appear. When the direction of spinning disc is reversed, the order of colors will also reverse. This principle is known as Subjective Color Illusion and is due to a psychological perceptive effect in the brain.