Impossible Colors
I very vividly remember the first time I saw a new color. I was a freshman at Indiana University at the time, browsing through the stacks of Wells Library. On the 6th floor of the library (currently being remodeled), I hit upon an old issue of the journal Philosophical Psychology, and in it I found an article by Paul Churchland entitled Chimerical Colors: Some Phenomenological Predictions from Cognitive Neuroscience. I'm ashamed to say that I have never found the time to dig into the article itself: too striking are the demonstrations its contains. See Frank Heile's response to this Quora question for a summary of the paper and a few of the figures.
To keep this post brief, I'll leave a few links for the reader to explore in addition to the links already mentioned.