If you have deutan color blindness, the world looks like it’s been filtered through a palette of mostly yellows, blues, and muddy greens. Reds fade into brownish or olive tones, greens and reds blur together, and many colors that look distinct to someone with normal vision appear nearly identical to you. About 6.5% of men and roughly 0.4% of women have some form of deutan deficiency, making it the most common type of color vision deficiency in humans.
How Deutan Vision Changes Color
People with normal color vision have three types of cone cells in the retina, each tuned to a different part of the light spectrum: short (blue), medium (green), and long (red). Deutan color blindness affects the medium-wavelength cones, the ones responsible for detecting green light. Depending on the severity, those cones either work poorly or are missing entirely.
The result is that the brain receives a lopsided signal. Without reliable green input, it can’t properly distinguish colors in the middle and long wavelength range. That covers a huge swath of everyday colors: reds, oranges, yellows, greens, and browns all start to overlap. Blues and yellows, on the other hand, stay relatively intact because they rely on the short-wavelength cones, which are unaffected.
Think of a rainbow. Where someone with typical vision sees a smooth gradient from red through orange, yellow, green, blue, and violet, a person with deutan vision sees something closer to a two-tone band. The red and green portions collapse into a brownish-yellow streak, while the blue end stays vivid. The transition zone in between looks washed out.
Deuteranomaly vs. Deuteranopia
Deutan color blindness comes in two forms, and the difference between them is significant. Deuteranomaly is the milder version, affecting about 5% of men. The green-sensing cones are present but contain a hybrid pigment whose sensitivity is shifted toward the red end of the spectrum. Because the green cones and red cones now respond to light in a very similar way, the brain has less contrast to work with. Greens look more reddish, and certain color pairs are harder to tell apart, but you still perceive a range of hues. The National Eye Institute describes deuteranomaly as mild enough that it typically doesn’t interfere with daily activities.
Deuteranopia is the more severe form, affecting about 1.5% of men and only 0.01% of women. In this case, the green-sensing cones are missing entirely, either because the gene was lost or because a hybrid gene produces a pigment so close to the red pigment that it provides no new information. The brain is left with only two functioning cone types (blue and red), reducing the entire color world to shades of blue and yellow. People with deuteranopia cannot distinguish red from green at all.
Colors That Get Confused
The everyday frustrations of deutan color blindness come down to specific color pairs that look identical or nearly so. These are the most common trouble spots:
- Red and green: The classic confusion. A red apple and a green apple can look like the same muddy brownish color. Traffic lights are distinguishable mainly by position, not color.
- Orange and red: These blend together, making it hard to tell a ripe tomato from an unripe one, or to distinguish between “caution” and “stop” signs at a glance.
- Green and brown: Leaves against tree bark, or a green shirt next to a brown one, can appear almost identical.
- Purple and blue: Because purple contains red (which is poorly perceived), it often looks like plain blue. A violet flower can appear just blue.
- Pale shades: Pastels and muted tones are especially difficult. A light pink can look like light gray, and a sage green may appear tan.
These confusions scale with severity. Someone with mild deuteranomaly might struggle only in poor lighting or with desaturated colors, while someone with deuteranopia faces these mix-ups constantly, in every setting.
Why It Mostly Affects Men
The genes responsible for green and red cone pigments sit on the X chromosome. Since biological males have only one X chromosome, a single defective copy is enough to cause color blindness. Biological females have two X chromosomes, so a working copy on the second chromosome typically compensates for a defective one on the first. This is why roughly 1 in 15 men has some form of deutan deficiency, while fewer than 1 in 200 women are affected.
One important feature of this inheritance pattern: fathers cannot pass X-linked traits to their sons, because sons inherit their single X from their mother. A color-blind father will pass the gene to all of his daughters, who become carriers. Those carrier daughters then have a 50% chance of passing it to each of their sons.
How It’s Diagnosed
The most widely used screening tool is the Ishihara plate test, a set of circular images made up of colored dots with a number hidden inside. If you have deutan color blindness, certain numbers will be invisible or appear as different numbers entirely. The test is quick and widely available in eye clinics and even in some school screenings.
The Ishihara test has a notable limitation, though: it’s good at detecting red-green deficiency but not very accurate at distinguishing whether the problem is deutan or protan (the other form of red-green color blindness, which affects the red cones instead). One validation study found the Ishihara test classified 33 people as deutan while a more precise digital test identified only 23 as deutan and reclassified 12 as protan. For a definitive diagnosis, newer computer-based tests like the Colour Assessment and Diagnosis (CAD) test or the Waggoner Computerized Color Vision Test can pinpoint the exact type and measure the severity on a numerical scale.
Practical Impact and Work Restrictions
For most people with deuteranomaly, the condition is a mild inconvenience. You learn to rely on context clues: the position of a traffic light rather than its color, labels on clothing, or asking someone to confirm whether something is green or brown. Smartphone apps and browser extensions can now shift colors in real time to make confusing pairs more distinguishable.
Certain careers do impose strict color vision requirements. Commercial aviation is one of the most regulated. As of 2025, the FAA requires pilots to pass an approved computer-based color vision test. Deutan pilots must score below a threshold of 6 on the red-green scale of the CAD test to qualify, a more lenient standard than the one applied to protan deficiency (which allows scores up to 12), because protan vision involves an additional dimming of red light that creates greater safety concerns. On the Waggoner test, deutan screening requires scoring at least 20 out of 32 on a dedicated deutan section.
Other fields with color vision requirements include electrical work (where wire color coding is critical), certain military roles, and some laboratory or quality control positions. The specific requirements vary, and many employers test on a case-by-case basis rather than imposing a blanket ban.
Living With Deutan Color Blindness
Color blindness is present from birth and doesn’t worsen over time. There is no treatment that restores normal color perception, though special filter glasses (like those from EnChroma) can increase contrast between certain colors for some people. These glasses work better for anomalous trichromats (those with shifted cones) than for dichromats (those missing cones entirely), because they enhance a signal that needs to exist in the first place.
Most people with deutan color blindness develop a reliable set of workarounds by early adulthood. The biggest challenges tend to be social rather than functional: not realizing a sunburn is forming, mismatching clothes, or missing color-coded information on charts and maps. Digital accessibility has improved significantly, with many apps and operating systems now offering colorblind-friendly display modes that replace red-green contrasts with blue-yellow or luminance-based alternatives.