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Colour blindness: seeing red and green differently
Last updated: 20 August 2026
'Are you colour blind?' — anyone who struggles with red and green hears the question regularly, and the word itself misleads. Hardly anyone sees in black and white; it is about colours sitting closer together than they do for others. For about one in twelve men that is daily reality. How it works, what you notice, and what practically follows.
In short
- You see colour with three cone types (red-, green- and blue-sensitive); in colour vision deficiency one type works differently or not at all.
- Red-green deficiency is by far the most common, is inherited (X chromosome) and mainly affects men (±8%; women ±0.5%).
- Complete colour blindness is extremely rare; most affected people see colours but distinguish certain shades less well.
- It cannot be cured, but with early recognition (school!), smart aids and sometimes a career check it is perfectly liveable.
⚠ Acute symptoms?Sudden vision loss, an eye injury, chemicals in the eye, severe pain, or new blind spots in your visual field? Don't wait for an online explanation — call your GP (huisarts), the out-of-hours GP service, or 112 immediately.
How colour vision works
The retina holds three types of cones, each sensitive to a different part of the light spectrum — roughly red, green and blue. The brain constantly compares the signals of the three and constructs the entire palette from them. If one cone type works at reduced strength (most common) or not at all, the ratios come out differently: certain colours that differ clearly for others arrive nearly identical.
In the red-green deficiencies — by far the largest group — red, green, brown, orange and olive shades slide towards each other. Blue-yellow deficiencies and complete colour blindness (everything in greys, usually with light sensitivity and poor acuity) also exist, but are rare to extremely rare.
Why mostly men?
The genes for the red- and green-sensitive pigments sit on the X chromosome. Men have one: a single altered copy suffices. Women have two and are only affected when both copies are altered — hence the skewed distribution: about 8% of men versus 0.5% of women. Women with one altered copy are carriers and can pass the trait on; the classic pattern is a grandfather 'handing' it via his daughter to his grandson.
Congenital colour vision deficiencies are stable: they get neither worse nor better. If colour vision noticeably changes later in life, or differs between the eyes, that is not colour blindness but a reason for an eye examination — acquired colour vision change can accompany retinal or optic nerve conditions.
How is it tested?
The best-known test is the Ishihara test: circles of coloured dots hiding a number that only normal red-green vision picks out fluently. It is fast and sensitive for detecting red-green deficiency, but says little about severity. For that, further tests exist: arrangement tests with coloured caps and — where it truly matters, as in certain occupational examinations — lantern tests or precise anomaloscope measurements.
Early detection is most valuable for children. Not because treatment is needed, but because school can accommodate it: colour-coded teaching methods, charts and maps put a child with red-green deficiency at an unnecessary disadvantage when nobody knows. A simple test when in doubt (often around age 6–7) prevents years of misunderstanding.
Practical: school, work, driving
Good news first: for an ordinary driving licence, colour vision is not an examination requirement in most countries, including the Netherlands. Some professions do set colour vision requirements — pilot, train driver, maritime service, certain police roles, and parts of aviation and electrical engineering (colour-coded wiring). Anyone nurturing such a career wish while in doubt is wise to take an official examination early, before an education track.
And the special 'colour blind glasses'? They can boost contrast between certain shades and some people enjoy them, but they do not confer normal colour vision and do not pass examinations. Often more practical: apps that name colours, good labelling (socks!), and colleagues or housemates who know that 'the green line' carries no information for you.
Frequently asked questions
My son fails the colour test at school. Now what?
No panic — have it confirmed with a proper test at an optometrist or ophthalmologist and above all inform the teacher. The main 'treatment' is that school and surroundings take it into account. Beyond that your son can do virtually everything his classmates can.
Can women really not have colour vision deficiency?
They can — it is just much rarer (about 1 in 200). Carriers sometimes have subtly altered colour vision. The blue-yellow variant affects men and women equally.
Colours have seemed duller to me these past years. Is that colour blindness?
No — congenital deficiencies do not change over life. Gradually duller or yellower vision fits cataract or other eye changes, and sudden colour change in one eye can accompany an optic nerve problem. Both warrant examination.
Is there a treatment or gene therapy?
For the common congenital forms there is no treatment; gene therapy is being researched for the rare severe forms but is not available care. The gains lie in adaptation, aids and timely information for study and career choices.
Sources and further reading
This article is general explanation, not medical advice about your situation. For acute symptoms: call your GP, the out-of-hours GP service, or 112.