Some people have seen that sort of "impossible" color: http://www.scientificamerican.com/article.cfm?id=seeing-forbidden-colors http://www.scientificamerican.co

Some people have seen that sort of "impossible" color: http://www.scientificamerican.com/article.cfm?id=seeing-forbidden-colors http://www.scientificamerican.com/article.cfm?id=seeing-forb... Basically if you have areas of different incompatible colors next to eachother, and they're the same subjective brightness, and you use fancy eye-tracking equipment to make the border stay in exactly the same place on your retina, then your brain gets confused and shows you some impossible combination around the boundary.