The size-color illusion

Slides were made from Munsell color chips in three sizes, four hues, and two chromas; all had the same intensity. A direct-comparisons, forced-choice procedure was used with 100 male and female volunteers from psychology courses. When pairs of slides had the same size and chroma, the order of decreasing apparent size was red-purple, yellow-red, purple-blue, and green. At chroma/8, all comparisons were significant except yellow-red over purple-blue. At chroma/4, the same order was found, but the effect was not pronounced. When pairs were made up of identical hues but different chromas, the square with chroma/4 (less saturation) appeared significantly larger.