A color illusion that strongly induces color contrast effect has been found by a research team at the Toyohashi University of Technology Department of Computer Science and Engineering, and Electronics-Inspired Interdisciplinary Research Institute (EIIRIS). The powerful visual illusion clarified a century-old contradiction relating to simultaneous color contrast theory. Through a human psychophysical experiment, the team demonstrated that the presence or absence of flanking contours formed from extremely thin white lines could be used to switch between contradictory visual phenomena, enabling consistent explanation for both discrepant theories. This solution alters theories of visual computation relating to color appearance, and is expected to contribute to industrial design and high-definition imaging.