Our perception of color enriches our lives immensely. Humans are very visually oriented creatures, and we depend on color as an environmental cue--say, to detect the ripeness of a fruit or the health of a family member--and use it as a signal--to indicate danger on a signpost, for instance. Those who are interested in the visual arts even celebrate the Pantone Color of the Year, whose selection by the famed graphics company is meant to capture the mood of the times and to influence fashion and interior décor for each cycle of the calendar. As fundamental as color is to our sensory experience, though, we may all actually see things very differently from each other. We can think of color vision in three layers: at the bottom, the biology of perception; above that, the way we talk about color; and at the top, how our color preferences emerge.
Our color vision is made possible by cone cells, which sit on the retina in the back of the eye. Each cone cell contains one of three types of pigment: pigment that best absorbs long-wavelength light (yellow-green), medium-wavelength light (green), or short-wavelength light (blue). These pigments can also absorb a small range of colors a bit less well, and their overlapping sensitivities grant to us a continuum of visible color, from red to violet. (The long-wavelength cone’s sensitivity extends into the red part of the spectrum, so this is sometimes referred to as the “red” cone rather than the “yellow-green” one.)
Further, we can divide this range into infinitesimally small slices: Humans can distinguish up to ten million colors within the visible spectrum. However, people who are color-blind¾who lack function in one or more types of cone, or who lack the cone altogether¾can perceive only a partial slice of the full spectrum: [figure 2]. The most common type of color blindness is the inability to distinguish between red and green, when either the medium- or long-wavelength-sensitive cone type is impaired or absent. Red-green color blindness occurs in 8% of men and 0.5% of women of North European descent, and at much lower rates in other groups. These rates were high enough to cause a small uproar at last week’s Jets-Bills football game, in which players sported all-green and all-red jerseys, respectively; color-blind viewers were unable to tell the teams apart.
On the other hand, color vision can also come with a bonus: Very rarely, people possess tetrachromacy, meaning that they have the three standard cone cell types, plus a fourth cone that appears to best absorb medium-to-low-wavelength light--red, orange, and yellow. Due to the way that some aspects of color vision are genetically inherited, only women have been found to exhibit tetrachromacy so far. Just a handful of such women have become aware of their condition and reported it to the scientific community; they appear to have a more nuanced experience of the color yellow, but it remains unclear how much their complete visual experience differs from the rest of ours.
Even among trichromats, or people with three functioning cone cell types and thus normal color vision, the ability to distinguish among different colors varies widely. To find out how chromatically discriminating you are, challenge yourself to choose which shade is different from the others or place colors along a spectrum.
Language of color
Color perception, for all the richness of its experience within individuals, would lose much of its meaning without its expression among people through language. We can’t be certain that any two people experience color in exactly the same way in the brain--the “green” that one person experiences by looking at the leaves on a tree may not be the same as what another person does. But we can at least assign a term to the color of a leaf in the summer, or to the color of light at a given wavelength, or to something else that is absolute.
Through history, human languages have each developed their own words for colors. Rather than appearing simultaneously, though, the same color terms tended to develop in clusters over time among many languages. Words for “light” or “white” and “dark” or “black” almost universally appeared first, often followed closely by red, then yellow and green, then blue, then brown, then finally gray, orange, pink, and purple. This paradigm is based on color terms in English, and it has some variation among languages. For instance, in Vietnamese, the words for “blue” and “green” are the same; they’re differentiated in conversation with prefixes and contextual clues. A greater departure from this pattern appears in the language of the OvaHimba people of northern Namibia, who use only four color terms: vapa to indicate white and yellow, buru for some shades of green and blue, dambu for some shades of brown, red, and other green shades, and zuzu for yet other shades of red, green, and blue, as well as for purple. On top of that, somewhat unsurprisingly, the OvaHimba have demonstrated much greater sensitivity to different shades of green than have any other studied cultures. It remains a mystery why this sensitivity hasn’t been demonstrated in other cultures.
Nearly everyone has one or a few favorite colors, with the exception of a lone PhDISH contributor who recently asked, “Wait, do people actually have favorite colors? I always thought that was just something you asked kids about to avoid long silences....” Among the rest of us, across many cultures, blue is consistently favored more often than other colors. (Those who are red-green color-blind, though, tend to prefer bright yellow instead, despite their ability to see blue!) It’s unclear why the preference for blue is so strong, although some hypothesize that we’re collectively drawn to the sky and the sea. Others postulate that, just as the term “blue” didn’t enter the collective vocabulary until after several other color terms did, perhaps humans couldn’t even perceive the color until briefly before its term appeared, and its novelty accounts for its favor. Evidence for this is found in ancient literature – Homer’s Odyssey records several references to a “wine-dark sea” rather than anything blue; other Greek writers describe other colors but never use “blue”; terms for “blue” are arguably absent in the Bible.
A puzzle remains: Does humanity name a color shortly after we develop ability to see it? Or have we always been able to see the entire rainbow, but failed to recognize and communicate all the colors until we’ve named them? Until science solves that mystery, we can only hope that the Pantone Color of the Year for 2016 will be an improvement over this year’s muddy-red marsala.
The Radiolab podcast episode on color.