Well, then I will borrow the words of the fraudster medium (who speaks with the dead) and yells at his audience when he doesn’t receive a hit from a session of cold readings, John Edward: “I’m not getting anything wrong – you’re just refusing to validate what I’m hearing from the other side!!” 🙂
That was my best guess. Another guess would be the interplay of the cone blue/yellow and red/green cone cells when stimulated by certain wavelengths of colors. There are many retinal cells which send signals to the brain based not only upon that they alone are stimulated, but also whether the surrounding cells are either stimulated or NOT stimulated. The relationship between the brain & retina is not and probably never will be fully understood. And sometimes things happen which illustrates this quite elegantly (hence the dress).