Types of Colour Blindness

Colour blindness is not a single condition — it encompasses several distinct types of colour vision deficiency (CVD), each caused by different abnormalities in the cone cells of the retina. Understanding the different types is important for accurate diagnosis, workplace accommodations, and designing accessible content.

The Two Main Categories

All forms of colour blindness fall into two broad categories:

Congenital (inherited) — present from birth, caused by genetic mutations
Acquired — developed later in life due to disease, injury, or medication

Within congenital CVD, there are three primary axes of deficiency based on which cone type is affected:

Protan (L-cone / red-sensitive)
Deutan (M-cone / green-sensitive)
Tritan (S-cone / blue-sensitive)

Red-Green Colour Blindness (Most Common)

Red-green CVD accounts for approximately 98% of all cases. It is caused by mutations on the X chromosome.

Protanopia

Mechanism: Complete absence of L-cones (long-wavelength / red-sensitive)
Prevalence: ~1% of males, under 0.01% of females
What they see: Reds appear very dark or black; cannot distinguish red from green; reduced sensitivity to the red end of the spectrum
Characteristic: The brightest point of the visible spectrum shifts toward yellow-green

Protanomaly

Mechanism: L-cones present but with reduced or shifted sensitivity
Prevalence: ~1% of males
What they see: Similar to protanopia but less severe; reds appear muted or brownish
Characteristic: Mild difficulty distinguishing red, orange, and green

Deuteranopia

Mechanism: Complete absence of M-cones (medium-wavelength / green-sensitive)
Prevalence: ~1% of males, under 0.01% of females
What they see: Similar to protanopia — confuses reds and greens — but without the reduced brightness of reds
Characteristic: Most common form of severe red-green CVD

Deuteranomaly

Mechanism: M-cones present but with shifted peak sensitivity
Prevalence: ~5% of males — the single most common form of colour blindness
What they see: Greens shifted toward red; difficulty distinguishing green from red, yellow from orange
Characteristic: Severity varies widely — some people have very mild anomalous trichromacy

Blue-Yellow Colour Blindness

Far rarer than red-green CVD, blue-yellow deficiencies affect the S-cones and are autosomal (carried on chromosome 7, not the X chromosome), meaning they affect men and women equally.

Tritanopia

Mechanism: Complete absence of S-cones (short-wavelength / blue-sensitive)
Prevalence: ~0.008% of the population (equally in men and women)
What they see: Blue appears as green; yellow appears as violet or light grey; confusion between blue and green, and between yellow and red
Characteristic: Often acquired rather than congenital

Tritanomaly

Mechanism: S-cones present but with reduced sensitivity
Prevalence: Extremely rare
What they see: Similar to tritanopia but milder
Characteristic: Often progressive if acquired

Complete Colour Blindness

Achromatopsia (Monochromacy)

Mechanism: Complete absence of cone function — only rod vision remains
Prevalence: ~1 in 30,000 people worldwide (no sex preference)
What they see: Only shades of grey — truly black-and-white vision
Associated symptoms: Severe light sensitivity (photophobia), reduced visual acuity (~20/200), involuntary eye movement (nystagmus)
Note: Most “colour blind” people are NOT achromatopes — true monochromacy is extremely rare

Blue Cone Monochromacy

Mechanism: Both L-cones and M-cones are non-functional; only S-cones and rods work
Prevalence: ~1 in 100,000 males
What they see: Very limited colour perception; primarily sees shades of blue with some grey
X-linked: Like red-green CVD, primarily affects males

Comparing the Types at a Glance

Type	Cone Affected	Prevalence (Males)	Severity	Can be Corrected?
Deuteranomaly	M-cone (shifted)	~5%	Mild–Moderate	Partially with filters
Deuteranopia	M-cone (absent)	~1%	Moderate–Severe	Partially with filters
Protanomaly	L-cone (shifted)	~1%	Mild–Moderate	Partially with filters
Protanopia	L-cone (absent)	~1%	Moderate–Severe	Partially with filters
Tritanopia	S-cone (absent)	~0.01%	Moderate	No
Achromatopsia	All cones	~0.01%	Complete	No

How to Find Out Which Type You Have

Online tests like the Ishihara Test and Farnsworth 100 Hue Test can indicate whether you have red-green CVD, but clinical tools like an anomaloscope are needed for definitive typing. The anomaloscope requires the user to match the colour of two halves of a field by adjusting a mixture of red and green light — the results precisely identify protanopia vs deuteranopia and the degree of severity.

For a preliminary indication, our Ishihara Test includes diagnostic plates that can suggest a protan or deutan pattern.

Frequently Asked Questions

Can you have more than one type of colour blindness? In rare cases, yes — a person can be affected by both red-green and blue-yellow deficiencies simultaneously. This is most common with acquired CVD caused by disease.

Is the most common form of colour blindness severe? No. Deuteranomaly (the most common type) is often quite mild. Many people with deuteranomaly are not even aware they have it until they are tested.

Can colour blindness be inherited from a grandfather? Yes — this is the classic inheritance pattern. A grandfather passes his X-linked CVD gene to his daughters, who become carriers, and then 50% of their sons inherit the condition.