“The difference in kind between our experience of red and our experience of green does not mirror any difference in kind in lightwaves in the worldthe wavelengths of light, which give rise to our perception of hue, form a smooth continuum. Red and green, perceived as qualitatively different properties are constructs of the chemistry and circuitry of our nervous system. They could be absent in an organism with different photopigments or wiring; indeed, people with the most common form of colorblindness are just such organisms.”

—Steven Pinker, The Blank Slate: The Modern Denial of Human Nature, 2002.