The color pink is commonly understood as a simple combination of red and white. While this description holds true for mixing paint, the scientific origin of pink is more complex. The perception of this color challenges the physical rules of light and reveals a sophisticated process within the human visual system. To understand pink, one must first examine the nature of color, which is rooted in light and wavelength.
The Physics of Color and Wavelengths
Color is fundamentally a perception created by the interaction between light waves and our eyes. Visible light is only a small section of the electromagnetic spectrum, ranging from approximately 380 nanometers (nm) to about 750 nm. Within this range, different wavelengths correspond to the spectral colors: red, orange, yellow, green, blue, and violet. Red light occupies the longest wavelengths in this visible band (typically between 620 nm and 750 nm). These single-wavelength colors, known as spectral colors, are what we see when white light is split by a prism, forming a continuous rainbow.
Pink’s Extra-Spectral Identity
Pink is not a spectral color, meaning no single wavelength of light corresponds to it. This unique status classifies pink as an extra-spectral hue that exists only as a combination of multiple wavelengths. Pink is perceived when the eye receives a mix of long-wavelength red light and short-wavelength light (like blue or violet), desaturated by white light. When a pink object absorbs most green and yellow light, it reflects significant red light and some short-wavelength blue/violet light. The resulting strong signals from opposite ends of the spectrum trigger the brain to perceive pink, which is best described as an unsaturated tint of red.
How the Brain Constructs Pink
Pink is constructed through neural processing within the human visual system. Our eyes contain three types of cone cells sensitive to short (blue), medium (green), and long (red) wavelengths. Signals from these cones are processed by the brain using the opponent process theory of color vision, which proposes three opposing neural channels: red versus green, blue versus yellow, and black versus white. Pink is constructed when the red-green channel is activated by a strong red signal from the long-wavelength cones, while the white light component activates the black-white channel, signaling high brightness. This combination of strong red activation and high lightness input, without the opposing green signal, leads the visual cortex to create the perception of pink.
Creating Pink in Different Color Systems
The technical creation of pink varies depending on whether light is being added or subtracted. In the Additive Color Model, such as the RGB system used in digital displays, pink is generated by combining red light with a lesser amount of blue and green light. For instance, a bright pink results from the maximum intensity of the red subpixel combined with a partial intensity of the blue and green subpixels, which lighten the red toward white.
In contrast, the Subtractive Color Model, used in pigments and printing (CMYK), creates pink by physical mixture. In CMYK, magenta is the closer extra-spectral equivalent to red. Pink is created by using a low concentration of magenta ink with little to no cyan, yellow, or black ink. When mixing paint, pink is achieved by diluting red pigment with a white pigment, which reflects all visible wavelengths, effectively desaturating the red to produce its lighter tint.