Red-green color blindness is by far the most common form of color vision deficiency, and within that category, deuteranomaly (a weakened sensitivity to green light) is the single most prevalent subtype. Roughly 8 percent of men and under 1 percent of women of Northern European descent have some form of red-green deficiency, making it one of the most widespread inherited sensory differences in humans. The condition has a genetic explanation rooted in the X chromosome, which also accounts for the stark gap between men and women, and the lived experience ranges from barely noticeable to genuinely disruptive depending on severity.
What Red-Green Color Blindness Actually Looks Like
People often assume that someone with red-green color blindness sees the world in grayscale or literally cannot see red and green at all. That is almost never the case. The vast majority of people with this condition are anomalous trichromats, meaning they still have three types of cone photoreceptors in their retinas, but one type is shifted in its sensitivity so that it overlaps too much with a neighboring type. The result is that certain shades of red, green, orange, brown, and yellow can look confusingly similar. A person with deuteranomaly, for example, might struggle to tell a ripe red apple from a green one, or find it difficult to distinguish between certain shades of brown and olive green. The colors are not absent from their world so much as compressed into a narrower range.
About 6 percent of males have anomalies in the genes on their X chromosome that lead to significantly decreased spectral separation between their middle-wavelength (green-sensitive) and long-wavelength (red-sensitive) cone photoreceptors.1ScienceDirect (Current Opinion in Behavioral Sciences). The known unknowns of anomalous trichromacy When those two cone types respond to light in nearly the same way, the brain receives less distinct information about whether something is reddish or greenish, and the person experiences the overlap as color confusion.
The Four Subtypes of Red-Green Deficiency
Red-green color blindness is not a single condition. It comes in four varieties, split along two axes: which cone is affected (the green-sensitive M-cone or the red-sensitive L-cone), and whether that cone is merely shifted or completely missing.
- Deuteranomaly: The M-cone is present but shifted toward the L-cone’s sensitivity range. This is the mildest and most common subtype, accounting for roughly half of all red-green color vision deficiencies. Many people with deuteranomaly go years without realizing they see colors differently.
- Deuteranopia: The M-cone is functionally absent. Retinal measurements of deuteranopes show only one photosensitive pigment in the red-green region of the spectrum where people with normal vision have two.2PubMed Central. Cone pigments in human deutan colour vision defects This makes the deficiency more severe than deuteranomaly.
- Protanomaly: The L-cone is present but shifted toward the M-cone’s range. This is less common than deuteranomaly but still part of the red-green family. People with protanomaly tend to see reds as more muted or brownish.
- Protanopia: The L-cone is missing entirely. Like deuteranopia, this is a more severe loss of color discrimination.
At the molecular level, these subtypes trace back to the genes that code for the L-cone and M-cone pigments. Research on families carrying multiple types of red-green deficiency has shown that protanomaly and protanopia both involve replacement of the normal red pigment gene with a fusion gene that blends red and green pigment sequences, while deuteranomaly involves extra green pigment genes and a different fusion gene.3PubMed Central. Molecular basis of abnormal red-green color vision: a family with three types of color vision defects In protanomaly versus protanopia, the protanomalous individual retained more of the red pigment DNA in the fusion gene than the protanopic individual, explaining the difference in severity. The deutan and protan subtypes feel similar in daily life, but they involve distinct genetic and photoreceptor changes.
Why Men Are So Much More Likely to Be Affected
The genes for both the M-cone and L-cone pigments sit on the X chromosome. Since men have only one X chromosome (paired with a Y), a single defective copy of either gene is enough to produce red-green color blindness. Women have two X chromosomes, so a functional copy on one can compensate for a defective copy on the other. A woman would need to inherit the defective gene from both parents to be affected, which is far less likely.
This inheritance pattern means about 8 percent of men experience red-green color vision deficiency, while the figure for women hovers around 0.4 to 0.5 percent.4PubMed. Worldwide prevalence of red-green color deficiency Women who carry one copy of the gene without being affected are carriers, and they can pass the trait to their sons. A carrier mother and a father with normal vision have roughly a one-in-two chance of producing a color-blind son with each pregnancy.
Prevalence Varies Across Populations
That 8 percent figure is not universal. It describes populations of European descent most reliably. Large population surveys put the prevalence of red-green deficiency in men of Chinese and Japanese ethnicity at roughly 4 to 6.5 percent, and rates in populations of African descent tend to be even lower.4PubMed. Worldwide prevalence of red-green color deficiency Studies confirm that red-green deficiency remains the most widespread form of color vision impairment across all populations studied, including diverse groups in regions like Northern India, even if the exact numbers differ.5Genes & Diseases. Prevalence and gene frequency of color vision impairments among children of six populations from North Indian region
The reasons for these population differences are not fully settled. Some researchers point to genetic drift and founder effects in populations that migrated through environments where color vision was under different selective pressures. Others note that methodological differences between studies, including the specific tests used and how participants were recruited, can inflate or deflate reported rates. What is consistent across all these surveys is the basic pattern: red-green deficiency dwarfs every other type, and men are affected at many times the rate of women.6PubMed Central. A Global Perspective of Color Vision Deficiency: Awareness, Diagnosis, and Lived Experiences
Rarer Forms of Color Blindness
Red-green deficiency dominates the conversation, but it is not the only kind. Blue-yellow deficiency, often called tritan deficiency, affects the short-wavelength (S-cone) system. Because the S-cone gene sits on chromosome 7 rather than the X chromosome, tritan deficiency is inherited in an autosomal dominant pattern and affects men and women at roughly equal rates. It is also much rarer, estimated at well under 1 percent of the general population. People with tritan deficiency confuse blues with greens and yellows with violets, a pattern quite different from the red-green confusion most people associate with color blindness.
At the extreme end sits achromatopsia, sometimes called complete color blindness. This is a rare autosomal recessive disorder of cone photoreceptor function that typically appears from birth and involves not just absence of color vision but also photophobia, involuntary eye movements, and reduced visual acuity.7Güncel Retina Dergisi (Current Retina Journal). Ocular Genetic Studies in Achromatopsia Achromatopsia affects roughly 1 in 30,000 to 50,000 people. Six genes have been identified as causes so far, and the condition represents a fundamentally different mechanism from the cone-pigment shifts that cause red-green deficiency. When people imagine “color blindness” as seeing entirely in shades of gray, they are actually picturing achromatopsia, which most people with color blindness do not have.
Color Vision Deficiency That Is Not Inherited
Not all color vision loss is genetic. Acquired color vision deficiency can develop later in life from certain medications, diseases, or simply aging. The pattern of acquired deficiency often differs from the inherited kind in revealing ways.
A systematic review of drug-induced color vision changes found that different medications affect different parts of the spectrum. Chloroquine and hydroxychloroquine, used for autoimmune conditions, tend to cause blue-yellow (tritan) defects at early stages of retinal toxicity and progress to red-green defects as damage advances. Digoxin, a heart medication, causes temporary red-green defects through its action on retinal cells. Ethambutol, used in tuberculosis treatment, tends to produce blue-yellow deficiency due to optic nerve damage. PDE-5 inhibitors like sildenafil can cause transient blue-tinted vision.8PubMed Central. Acquired Dyschromatopsia and Its Link to Drug Toxicity Most drug-induced color vision changes are reversible when the medication is stopped, with the notable exception of chloroquine and hydroxychloroquine toxicity, which can cause permanent damage.
Aging also gradually degrades color perception, particularly in the blue end of the spectrum, as the lens yellows over decades. Cataracts, diabetes, and neurological conditions like multiple sclerosis can all affect color vision. These acquired changes are clinically important because they may serve as early warning signs of broader eye or neurological damage. Unlike inherited red-green deficiency, acquired dyschromatopsia can be asymmetric, affecting one eye more than the other, and can change over time.
How Color Blindness Gets Detected
The most familiar screening tool is the pseudoisochromatic plate test, a set of printed circles filled with colored dots that form a number visible to people with normal color vision but hidden or altered for those with a deficiency. The Ishihara test, introduced in 1917, remains the most widely used version. These plate tests provide one of the simplest methods of distinguishing between normal and deficient red-green color perception.9JAMA Ophthalmology. Tests for Color Deficiency Based the Pseudoisochromatic Principle: A Comparative Study of Several New Tests
Plate tests are good at catching whether you have a red-green deficiency, but they are not great at measuring exactly how severe it is or distinguishing precisely between subtypes. For that, clinicians use arrangement tests (like the Farnsworth-Munsell 100 Hue Test, where you sort colored caps into order) or anomaloscopes (instruments that ask you to match two halves of a bipartite field by mixing wavelengths of light). The anomaloscope is considered the gold standard because it directly measures how your cone photoreceptors respond to specific wavelengths. Many people discover their color deficiency through routine screening in school or during an occupational examination, which is why the simpler plate tests remain the first line of detection.
Living With Red-Green Color Blindness
For people with mild deuteranomaly, color blindness may amount to little more than occasional embarrassment about mismatched clothing or trouble reading color-coded charts. But research consistently shows that the condition has measurable effects on daily life, work, and emotional wellbeing. An integrative review of studies on quality of life found that people with color vision deficiency face challenges in multiple areas of daily life, especially work-related activities.10PubMed. The impacts of abnormal color vision on people’s life: an integrative review
A validated questionnaire measuring quality of life specifically for color-blind individuals found that people with the condition reported significantly greater negative impacts on their health and lifestyle, their work, and their emotional life compared to people with normal color vision.11PubMed Central. Development and validation of a questionnaire assessing the quality of life impact of Colour Blindness (CBQoL) The work domain is where many people feel the impact most keenly. Certain careers restrict or exclude people with color vision deficiency, including commercial aviation, some military roles, electrical work (where wire colors matter), and specific laboratory positions. Even in careers without formal restrictions, tasks like interpreting color-coded data, reading traffic signal positions by color alone, or assessing whether food is cooked can be quietly frustrating.
The emotional and social effects are often underappreciated. A study of Malaysian adolescent boys with congenital color vision deficiency found that they scored significantly higher on measures of internalizing problems like withdrawal and anxiety, as well as externalizing problems including attention difficulties and aggressive behavior, compared to peers with normal color vision.12PLoS One. Behavioural and emotional assessment of Malaysian adolescent boys with congenital colour vision deficiency and its association with socioeconomic factors The researchers found elevated scores across six specific behavioral scales. Color blindness is sometimes treated as a trivial curiosity, but for young people trying to navigate schoolwork, social situations, and career aspirations, it can be a genuine source of stress.
Do Color-Correcting Glasses Actually Work?
If you have spent any time on social media, you have probably seen emotional videos of people trying on EnChroma glasses and apparently seeing vivid colors for the first time. The reality is more complicated than those videos suggest. EnChroma and similar products use notch filters that selectively block certain wavelengths of light between the red and green sensitivity peaks. The idea is that by removing the wavelengths where the shifted cone types overlap, you improve the contrast between the signals your brain receives.
Independent testing has found that these filters can shift color perception and may make some colors appear more vivid or distinct to some users. But controlled studies tell a more sobering story. One study found that while EnChroma glasses improved discrimination for some colors, they worsened discrimination for others, and the overall results did not support the use of notch filters for improving color discrimination in people with color vision deficiency.13PubMed. Do EnChroma glasses improve performance on clinical tests for red-green color deficiencies? A separate investigation concluded that it is not possible for these types of filters to truly improve wavelength discrimination for dichromats, though the filters can introduce brightness cues that allow some users to “cheat” on certain color vision tests without actually gaining new color perception. Claims of “curing color blindness” or allowing people to “see new colors” were not supported by the data.14Investigative Ophthalmology & Visual Science. Effect of “color-correcting glasses” on chromatic discrimination in subjects with congenital color vision deficiency
That said, some anomalous trichromats (people who still have three cone types but with a shifted one) do report a subjectively improved experience with certain filters, particularly in brightly lit outdoor conditions. The glasses are not doing nothing; they are changing the light that reaches your eye, which can make the world look different. Whether “different” equals “better” or “more accurate” depends on the individual and the specific viewing conditions. For people with more severe deficiencies like dichromacy, the glasses have less to work with.
Gene Therapy and the Prospect of a Cure
The most striking demonstration that color vision can be restored came from a gene therapy experiment in adult squirrel monkeys. These New World monkeys are naturally red-green color blind: they have only two types of cone pigment where Old World primates have three. Researchers injected a virus carrying the gene for the missing L-cone pigment into the monkeys’ retinas. About 20 weeks after treatment, the monkeys’ behavior on color discrimination tests changed dramatically, with their thresholds for distinguishing blue-green and red-violet stimuli dropping to levels consistent with trichromatic vision.15PubMed Central. Gene therapy for red-green colour blindness in adult primates The result was remarkable not just because the therapy worked, but because it worked in adults. The brain was able to interpret an entirely new color signal from cone cells that had never existed before, without any rewiring during a critical developmental window.
Translating this to humans is a different challenge. Human retinas are much larger, the gene delivery would need to reach a broader area, and the regulatory and safety hurdles are substantial. Several research groups are pursuing clinical trials for achromatopsia, the rarer and more severe form of complete color blindness, partly because the unmet medical need is greater and partly because the target genes are well-characterized. For the far more common red-green deficiency, the path to gene therapy is less clear, in part because the condition is not disabling enough to justify the risks of retinal surgery for most affected people. Still, the primate work established a proof of concept that the adult visual system is more plastic than anyone previously assumed.
Why Trichromacy Evolved in the First Place
Most mammals have only two types of cone photoreceptor and are, by human standards, red-green color blind. Trichromatic color vision, with separate red-sensitive and green-sensitive cones, appears to have evolved in the primate lineage. The leading hypothesis is that trichromacy gave our ancestors an advantage in detecting ripe fruits and young leaves against a background of mature foliage. Research on South American primates, some of which are polymorphic for color vision (with some individuals being trichromatic and others dichromatic within the same species), found that the spectral positioning of trichromatic cone pigments was well matched to the task of detecting fruits against leaves.16PubMed Central. Fruits, foliage and the evolution of primate colour vision
Molecular analysis of ancestral opsin genes suggests that the ancestors of both Old World and New World monkeys lacked a separate green pigment gene, and that the green-sensitive opsin later evolved from the red-sensitive one through gene duplication.17PubMed. Color vision of ancestral organisms of higher primates The same research raised an intriguing possibility: the red/green opsin gene seems to have survived a long nocturnal phase of mammalian evolution and remained under strong evolutionary pressure even in animals living in dark environments, suggesting it may serve some function beyond color vision, possibly related to circadian rhythms. This evolutionary history helps explain why red-green color blindness is so common. The M-cone and L-cone genes sit right next to each other on the X chromosome, arose from duplication, and share a high degree of sequence similarity. That proximity and similarity makes them prone to misalignment during cell division, which creates the gene deletions and fusion genes responsible for red-green deficiency.
John Dalton’s Eyes
The scientific study of color blindness has an unusually personal origin story. In 1794, the chemist John Dalton published the first known scientific description of color blindness, based on his own experience. He confused scarlet with green and pink with blue, and he correctly noted that his brother had the same condition, an early clue to its hereditary nature. Dalton’s own explanation was that his vitreous humor must be tinted blue, filtering out longer wavelengths before they reached his retina. He left instructions for his eyes to be examined after his death, but the post-mortem examination found perfectly clear eye fluids, ruling out his hypothesis.
The real answer had to wait nearly 150 years. DNA extracted from Dalton’s preserved eye tissue, still stored at the Manchester Literary and Philosophical Society, revealed that he was a deuteranope, missing the M-cone pigment entirely.18PubMed. The chemistry of John Dalton’s color blindness This finding contradicted the earlier belief of Thomas Young, who had suggested Dalton was a protanope (missing the L-cone instead). The diagnosis was confirmed to be consistent with the historical record of Dalton’s color confusions. Dalton’s legacy persists in the word “daltonism,” still used in several languages as a synonym for color blindness, and his case remains one of the earliest and most thoroughly investigated examples of the condition in the historical record.