Red-Green Color Blindness: Causes, Types and Daily Life

What is red-green color blindness?

In red-green color blindness, the light-sensitive cells in the retina that handle red and green work differently than usual. People still see colors, but some shades look alike: red and green, orange and yellow-green, brown and dark green, or pink and gray. Even though it is called color blindness, most people with it are not blind to color – they just see certain colors less distinctly.

It is by far the most common color vision deficiency. Among people of Northern European descent it affects about 8% of men and 0.5% of women.

What causes red-green color blindness?

The retina contains three kinds of cones – cells for color vision in daylight. Each type responds most strongly to one part of the light spectrum: short wavelengths (blue, "S"), medium (green, "M") and long (red, "L"). The brain compares their signals to work out color.

In red-green color blindness, either the red or the green cones are altered or missing. Their sensitivity curves move closer together, so the brain gets a weaker difference between the red and green signals – and has a harder time telling those colors apart.

Types of red-green color blindness: protan and deutan

In the "-anomaly" types all three cone types are present, but one is shifted – the deficiency can be mild, moderate or strong. In the "-anopia" types one cone type is missing completely. A typical sign of the protan types: red also looks darker, so a red traffic light or tail light appears dimmer.

Is red-green color blindness genetic?

Inherited red-green color blindness is X-linked recessive. The genes for the red and green cone pigments sit on the X chromosome. Men have only one X chromosome – if the gene is altered, they are affected. Women have two, and a working copy usually makes up for the altered one. That is why men are affected far more often.

• If a mother is a carrier, each son has a 50% chance of being color blind.
• A color blind father passes the gene to all of his daughters (they become carriers) but to none of his sons.
• A woman is only affected if both of her X chromosomes carry the gene.

Less often, color vision changes later in life – from eye or optic nerve disease or as a side effect of medication. If your color vision suddenly changes, see an eye doctor.

How to test for red-green color blindness

The best-known screening is the Ishihara test: numbers made of colored dots are hidden in a dot pattern, and people with red-green color blindness miss some of them or read a different number. You can take one free online here. For a full diagnosis, eye doctors also use instruments such as the anomaloscope, which measures how strong the deficiency is.

In children it often shows up at school – see our color blind test for kids.

Can red-green color blindness be cured?

Inherited red-green color blindness cannot be cured and does not change over a lifetime. Gene therapies are being researched but are not available. There are aids, though: color blind glasses can boost the contrast between red and green for many people, but they do not restore normal color vision.

Living with red-green color blindness

• Clothes: use labels or sort your wardrobe by color families.
• Food: ripeness of fruit, how well meat is cooked or ketchup on fries can be tricky.
• Charts and status lights: ask for symbols, patterns or labels instead of red/green only.
• Phone: iOS and Android offer color filters for protan and deutan in their accessibility settings.
• Driving: traffic lights can also be read by position. In the US, color blindness does not prevent you from getting a regular driver's license; commercial licenses require recognizing red, green and amber signals.

Some jobs – such as pilot, electrician or certain military roles – may require normal color vision. If you are aiming for one, check your color vision early.

Want to see what it actually looks like? Read what do color blind people see?