When teams of researchers tried to re-create Crane and Piantanida's revolutionary experiments with impossible colors, they often came up with disappointing results. Instead of seeing brand-new hues of greenish-red or blueish-yellow, subjects most frequently described the blended color as mud-brown [source: Wolchover]. Others would see fields of green with pixelated red dots scattered across it. Impossible colors became a scientific joke.
But in 2010, impossible colors were back in the headlines. This time, a pair of visual researchers from the Wright-Patterson Air Force Base in Ohio, believed they had determined why Crane and Piantanida had succeeded where others had failed.
In a Scientific American article, biophysicists Vincent Billock and Brian Tsou identified the combination of eye tracking and luminance (brightness) as key to tricking the brain into seeing impossible colors [source: Billock and Tsou].
Billock and Tsou ran their own experiments in which subjects were again strapped to a chinrest and monitored by the latest retinal tracking technology. With the images stabilized to the subjects' eye movements, Billock and Tsou played with the brightness or luminance of the two opposing color stripes.
If there was a difference in brightness, the subjects experienced the pixelated colors reported in earlier experiments. But if the two colors were equiluminant — exactly the same brightness — then six out of seven observers saw impossible colors [source: Billock and Tsou]. Even better, two of them could see the new colors in their minds for hours after the experiment was over.