The rarest form of color blindness is achromatopsia, or total color blindness, affecting roughly 1 in 30,000 to 33,000 people worldwide. People with this condition see entirely in shades of gray. Close behind in rarity is tritanopia, a blue-yellow deficiency that affects about 1 in 30,000 to 50,000 people. Both are dramatically less common than red-green color blindness, which affects about 8% of men.
How Rare Types Compare to Common Ones
Most color blindness falls into the red-green category. Around 8% of men and 0.5% of women have some form of it, making it extraordinarily common by comparison. Within that group, the breakdown is roughly 5% of men with a milder form (deuteranomaly, where green perception is shifted), 1% with a milder red-shifted form, 1% fully missing green cone function, and 1% fully missing red cone function.
Blue-yellow deficiency and total color blindness occupy a completely different tier. Where red-green color blindness affects 1 in 12 men, tritanopia and achromatopsia each affect fewer than 1 in 30,000 people. That makes them roughly 2,500 times less common.
There’s an important genetic reason for this gap. Red-green color blindness is linked to the X chromosome, which is why it disproportionately affects men (who have only one X chromosome, so a single faulty gene copy causes the condition). Blue-yellow deficiency and achromatopsia are not X-linked, so they show no strong gender bias. They’re simply uncommon across the board.
Achromatopsia: Complete Color Blindness
Achromatopsia is the most extreme form of color vision deficiency. People with this condition have cone cells in the retina that either don’t function or are entirely absent. Since cones are responsible for both color perception and sharp central vision in bright light, losing them affects far more than just color.
The condition typically comes with severe light sensitivity, because the eye relies entirely on rod cells, which are designed for dim-light vision and become overwhelmed in daylight. Involuntary eye movements (a constant, slight wobbling of the eyes) and reduced visual sharpness are also characteristic. Many people with achromatopsia wear dark-tinted lenses outdoors and struggle with tasks that require fine detail, like reading small text. The condition is present from birth and remains stable throughout life.
Genetically, achromatopsia traces back to mutations in genes that build the signaling machinery inside cone cells. Two genes account for the majority of cases. Mutations in these genes prevent cones from converting light into electrical signals the brain can interpret, effectively silencing the cone system entirely. The condition is autosomal recessive, meaning a child must inherit a faulty copy from both parents to be affected.
The Pingelap Island Exception
One striking exception to achromatopsia’s rarity exists on Pingelap Atoll, a tiny island in the Pacific. Around 1775, a typhoon and subsequent famine devastated the population, leaving only a handful of survivors. One of those survivors carried the gene for achromatopsia. Because the island’s population rebuilt from that tiny genetic pool, the condition became remarkably concentrated. Today, nearly 10% of Pingelap’s population has complete color blindness, and about 30% are carriers. Almost every case on the island traces back to that single male survivor.
Tritanopia: Blue-Yellow Deficiency
Tritanopia involves the loss or malfunction of the short-wavelength cones, which are the cells responsible for detecting blue and violet light. The gene that builds the light-sensitive protein in these cones sits on chromosome 7 (not a sex chromosome), which is why tritanopia affects men and women at similar rates.
Known mutations in this gene change a single building block in the blue-sensitive protein, rendering it partially or completely nonfunctional. Without a working protein, the cone cells either die prematurely or fail to transmit signals to the brain. The result is difficulty distinguishing blue from green and yellow from violet. Unlike red-green color blindness, where the world looks shifted but still colorful, tritanopia collapses the blue-yellow axis of color, making certain everyday distinctions surprisingly hard: telling a blue pen from a black one, for instance, or reading colored text on certain backgrounds.
There’s also a milder version called tritanomaly, where the blue cones are present but have a shifted sensitivity. People with tritanomaly can still perceive blue, but it appears weaker or slightly off. Both forms are extremely rare.
Why Standard Screening Misses Rare Types
If you’ve ever taken a color blindness test, it was almost certainly an Ishihara plate test, the one with colored dots hiding a number. These plates are designed exclusively to detect red-green deficiency. They cannot identify blue-yellow deficiency or total color blindness, and they can’t distinguish between different subtypes even within the red-green category.
This means someone with tritanopia could pass a standard screening and never realize they have a color vision deficiency. Detecting blue-yellow and complete color blindness requires different tools. A test that uses colored chips arranged in a sequence (like the Farnsworth-Munsell 100-hue test) can reveal blue-yellow errors by showing which part of the color spectrum a person confuses. A more comprehensive evaluation pairs a reflected-light test (colored plates or chips) with an instrument that uses projected light, like an anomaloscope. Together, these can classify the exact type and severity of a deficiency.
Because Ishihara plates are the default in schools and workplaces, rare forms of color blindness are almost certainly underdiagnosed. If you suspect you have difficulty with blue-yellow distinctions specifically, you’d need to request a more comprehensive evaluation.
Acquired Color Blindness Later in Life
Not all rare color blindness is inherited. Blue-yellow deficiency in particular can develop later in life as a result of disease, aging, or medication. Macular degeneration, glaucoma, diabetes, retinitis pigmentosa, and Alzheimer disease can all damage the retina or visual processing pathways in ways that preferentially affect blue-yellow discrimination. Certain medications and industrial chemicals can do the same.
Acquired color blindness differs from the inherited form in a few key ways. It can worsen over time, it may affect one eye more than the other, and its severity often fluctuates with the underlying condition. It also tends to appear as a blue-yellow deficiency regardless of the cause, because the short-wavelength cone system appears more vulnerable to damage than the red-green system. This means that while inherited blue-yellow color blindness is extremely rare, the acquired version may be more common than prevalence figures suggest, particularly among older adults with chronic eye conditions.