The experience of seeing color feels universal, yet the question of whether we all perceive the same colors remains complex. Color is not an inherent property of an object, but rather a sensory experience constructed by the brain in response to light. It exists at the intersection of objective physics—the energy and wavelength of light—and subjective biology, which involves how an individual’s visual system processes that light. This dichotomy frames the inquiry into color perception: How much is a shared reality based on physics, and how much is a private interpretation shaped by genetics, language, and context?
The Physics and Physiology of Color
Color perception begins with light, which is a form of electromagnetic radiation defined by its wavelength. The visible spectrum, which humans can perceive, ranges approximately from 400 nanometers (violet) to 700 nanometers (red). When light reflects off an object and enters the eye, it passes through the cornea and lens to reach the retina at the back of the eye.
The retina contains specialized photoreceptor cells, including the cones, which are responsible for color vision in bright light. Humans typically have three types of cones, leading to what is called trichromatic vision. These cones are differentiated by the photopigment they contain, known as opsin, which makes them sensitive to different ranges of wavelengths.
These three cone types are broadly categorized as Short-wavelength (S-cones), Medium-wavelength (M-cones), and Long-wavelength (L-cones). The S-cones absorb light best in the blue-violet region, the M-cones in the green-yellow region, and the L-cones in the yellow-red region. Seeing a specific color is not due to a single cone type firing, but rather the brain comparing the ratio of signals received from all three cone types. For example, light perceived as yellow stimulates both the L-cones and M-cones almost equally. This ratio-based signaling mechanism, involving three cone types, is the common structure shared across people with typical color vision.
Biological Basis for Variation
Individual differences in trichromatic vision start at the genetic level with the opsin genes. The genes responsible for the L- and M-cone opsins are located on the X chromosome and are prone to genetic variation. Subtle changes, known as single nucleotide polymorphisms (SNPs), can alter the opsin protein’s amino acid sequence, shifting the cone’s peak sensitivity.
For people with otherwise typical color vision, a common variation involves the L-cone opsin, where a single amino acid difference can shift the cone’s peak sensitivity by a few nanometers. This means two individuals may have slightly different spectral sensitivities for red and green light. This genetic variability is a biological source of subtle perceptual difference even among those considered “color normal.”
More pronounced genetic variations lead to forms of color vision deficiency, commonly known as color blindness, which often involve the L and M opsin genes. Red-green color confusion results from a missing or non-functional gene, or a hybrid gene causing the L- and M-cones to have highly overlapping spectral sensitivities. This reduces the number of independent color signals, making it difficult to distinguish between reds, greens, and mixed colors.
A rare, opposite variation is tetrachromacy, which is theorized to occur in some women who possess a unique fourth type of cone. Having four distinct cone types could theoretically allow a person to distinguish between hues that appear identical to a standard trichromat. This phenomenon represents the extreme end of biological variation, where the physical ability to capture light data is fundamentally different.
Influence of Language and Culture
Beyond the biological hardware, the brain’s “software”—specifically language and cultural categorization—affects how we process and organize color information. The concept of linguistic relativity, or the Sapir-Whorf hypothesis, suggests that the language we speak influences our perception and thought, a relationship often studied through color.
Languages vary significantly in the number of basic color terms they employ. Some languages, like Dani, traditionally use only two terms (“mili” for dark/cool and “mola” for light/warm), while others use a full set of eleven terms. Studies show that the number of available color words in a language can impact cognitive tasks like memory and reaction time.
When two colors fall on either side of a linguistic boundary, such as blue and green in English, speakers categorize them more quickly than two equally different colors within the same category, like two shades of blue. This suggests that the verbal label enhances the perceived difference between the hues, effectively sharpening the color boundary in the mind.
Research comparing different language groups, such as Russian speakers who have separate basic terms for light blue (‘goluboy’) and dark blue (‘siniy’), has demonstrated this effect. These speakers are often faster at discriminating between light and dark blue shades than English speakers, who categorize both under the single term “blue.” This shows that while the physical color itself is seen similarly, the cognitive framing and ease of recall are influenced by the language’s categorical structure.
Contextual Interpretation and Subjectivity
Even with identical eyes and a shared language, color perception is not fixed, as the brain constantly adjusts its interpretation based on context and environmental factors. One powerful example is simultaneous contrast, where an object’s color is altered by the color of its immediate surroundings.
A gray square will appear lighter against a dark background, but darker against a light background, despite its physical color remaining unchanged. The visual system exaggerates the differences between adjacent areas, which helps delineate edges and features but introduces subjectivity. This relative processing means the sensation of a color depends entirely on what is next to it.
Lighting conditions introduce another variable, leading to the phenomenon of metamerism. A metameric pair consists of two objects that appear the same color under one light source, such as daylight, but appear different under another, like fluorescent light. This occurs because the objects have different spectral reflectance curves, meaning they absorb and reflect light differently across the spectrum.
Finally, the brain applies a process called color constancy, which attempts to stabilize the perceived color of an object despite changes in the light source. For example, a red apple still appears red whether viewed under the warm light of an incandescent bulb or the cooler light of a winter sky. The brain “fills in” the expected color based on memory and expectation, often leading to perceptual disagreements when the context is ambiguous, as famously demonstrated by “The Dress” illusion.