Astute Chad’s News readers already know that colors correspond to various wavelengths of light, as shown when white light is run through a prism or when it forms a rainbow. But the reality is that colors only exist in our minds—the brain takes the output from the eye and interprets it as color. This becomes obvious when we take a closer look at the color magenta (also known as pink). Magenta/pink does not have a related wavelength and does not appear in a rainbow or prism. Yet we still “see” it. The linked article explains why.
Update: Ars Technica has an article that clarifies some of the internet hysteria over this topic.