The top prize of the contest, sponsored by the Neural Correlate Society, was awarded to Belgium’s Mark Vergeer for “Splitting Colors.”
The contest website explains:
The Splitting Color illusion is all about how we perceive colors. We start off with two identical, flickering colored stripes that remain unchanged throughout the demonstration. However, different surroundings will make these stripes appear completely different. When the stripe is flanked by a yellow/blue pattern, drifting to the left, it changes appearance, and looks red and cyan, drifting to the right, while the same stripe, flanked by a red/cyan pattern drifting to the right, suddenly looks yellow and blue, drifting to the left. This illusion shows that one and the same object can look completely different depending on its surroundings.
Much of this illusion has to do with how the brain changes its assumption about colors when contrasts and surrounding colors change relative to the entire visual field. Like changes to brightness, context matters in perception.