- Key People:
- John Dalton
- George Wald
- On the Web:
- RMIT Open Press - Colour Theory: Understanding and Working with Colour - Colour blindness (Oct. 30, 2026)
colour blindness
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What is colour blindness?
Color blindness, or color vision deficiency, is the inability to distinguish one or more of the three colors red, green, and blue. Most people have a weak color-sensing system rather than a total loss of color sensation.
There are different types of color blindness: dichromacy (two cone types functional) and monochromacy (none or only one cone type functional). Dichromatic individuals are ordinarily unable to distinguish between red and green.
Hereditary red-green color blindness is more common in males. Blue-yellow color blindness is not sex-linked and needs only one copy of the defective gene from either parent to be expressed. Acquired color blindness is usually the blue-yellow type and is often associated with chronic disease.
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How does colour blindness affect the way people see colours?
Color blindness, or color vision deficiency, affects how individuals perceive colors. Most people with color vision problems have a weak color-sensing system rather than a total loss of color sensation.
There are different types of color blindness. Dichromacy occurs when only two cone types are functional, while monochromacy occurs when none or only one type of cone receptor is functional. Dichromatic individuals are ordinarily unable to distinguish between red and green. Those with protanopia are blind to red, while those with deuteranopia are blind to green. Some people experience anomalous dichromatic conditions, which involve only minor reductions or weaknesses in color sensitivity.
People with color-defective vision don't have as good wavelength discrimination as those with normal vision and see many colors as identical that people with normal vision see as different.
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What are the most common types of colour blindness?
The most common types of color blindness are generally divided into dichromacy and monochromacy. Dichromacy occurs when only two cone types are functional, while monochromacy occurs when none or only one type of cone receptor is functional.
Common types of color blindness:
* Red-green color blindness Those with red-green color blindness have difficulty distinguishing between red and green.
* Protanopia Individuals with protanopia are blind to red because they lack red cones, leaving only blue and green light-absorbing cones.
* Deuteranopia Those with deuteranopia are blind to green because they lack green cones, but their blue and red cones are functional.
* Blue-yellow color blindness Some individuals experience blue-yellow color blindness. Tritanopia (blindness to blue) occurs when blue cones are absent, making it difficult to distinguish between blue and yellow.
* Monochromacy People with monochromacy, or complete color blindness, have deficiencies in visual acuity. This condition includes achromatopsia (complete absence of functional cone photopigments) and cone monochromacy (when two of the three cone types are nonfunctional).5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What causes colour blindness in people?
Color blindness is typically the inability to distinguish between certain colors, most commonly red and green. It arises from issues with the cones, which are specialized visual cells in the retina that perceive color.
There are different types of color blindness. Dichromacy occurs when only two cone types are functional, while monochromacy occurs when none or only one type of cone receptor is functional.
Color blindness can be inherited or acquired. The hereditary form of red-green color blindness is a sex-linked recessive trait, meaning it is more common in males because the genes responsible are carried on the X chromosome. Acquired color blindness, often of the blue-yellow type, can result from diseases like macular degeneration, or from certain drugs or chemicals.
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How can colour blindness be diagnosed?
Color blindness is typically diagnosed using specialized instruments that test a person’s ability to distinguish between different hues in the visible light spectrum. People with partial color blindness, such as those with red-green color blindness, may be unaware of their condition until tested with these instruments. In the retina, humans have three types of cones that function in the perception of color. One type absorbs light best in wavelengths of blue-violet, another in the wavelengths of green, and the third type is most sensitive to longer wavelengths, particularly red. Normal color vision, where all three cone types function correctly, is known as trichromacy. Defective color vision affects men more often than women. Total color blindness is extremely rare and is nearly always associated with poor vision in ordinary light and with nystagmus.
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How do people with colour blindness adapt to daily life?
Color blindness, or the inability to distinguish between certain colors, varies in type and severity. Most individuals with color vision deficiency have a weak color-sensing system rather than a total loss of color sensation.
People with color blindness adapt to daily life in various ways. They may rely on cues like brightness and saturation to differentiate colors. Others memorize the order of objects, like traffic lights, to navigate their surroundings effectively. Assistive technologies, such as color-correcting glasses or smartphone apps that identify colors, can also aid in daily tasks.
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colour blindness, inability to distinguish one or more of the three colours red, green, and blue. Most people with colour vision problems have a weak colour-sensing system rather than a frank loss of colour sensation. In the retina (the light-sensitive layer of tissue that lines the back and sides of the eyeball), humans have three types of cones (the visual cells that function in the perception of colour). One type absorbs light best in wavelengths of blue-violet and another in the wavelengths of green. The third type is most sensitive to longer wavelengths—more sensitive to red. Normal colour vision, when all three cone types are functioning correctly, is known as trichromacy (or trichromatism).
Types of colour blindness
There are several different types of colour blindness, which may be subdivided generally into dichromacy (dichromatism), when only two cone types are functional, and monochromacy (monochromatism), when none or only one type of cone receptor is functional. Dichromatic individuals are ordinarily unable to distinguish between red and green. Blindness to red is known as protanopia, a state in which the red cones are absent, leaving only the cones that absorb blue and green light. Blindness to green is known as deuteranopia, wherein green cones are lacking and blue and red cones are functional. Some persons experience anomalous dichromatic conditions, which involve only minor reductions or weaknesses in colour sensitivity. In protanomaly, for example, sensitivity to red is reduced as a result of abnormalities in the red cone photopigment. In deuteranomaly, in which sensitivity to green is reduced, the green cones are functionally limited. Two forms of blue-yellow colour blindness are known: tritanopia (blindness to blue, usually with the inability to distinguish between blue and yellow), which occurs when blue cones are absent; and tritanomaly (reduced sensitivity to blue), which arises from the abnormal function of blue cones.
Monochromacy, or complete colour blindness, is sometimes accompanied by deficiencies in visual acuity. Such conditions are rare and include achromatopsia (or rod monochromacy; the complete absence of functional cone photopigments) and cone monochromacy (when two of the three cone types are nonfunctional).
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Inherited and acquired colour blindness
Hereditary red-green colour blindness occurs mainly in males and Caucasian persons, with about 8 percent of men and 0.5 percent of women of European ancestry inheriting the conditions. Its predominance in males is due to the fact that red-green colour blindness is a sex-linked recessive characteristic, carried on the X chromosome. Hence, the trait for red-green colour blindness is passed from mother to son, from mother to daughter, or from mother and father to daughter. A son who inherits the trait from a carrier mother will be red-green colour blind (males inherit only one X chromosome, directly from the mother). A daughter who inherits the trait from a carrier mother (with a normal father) will have normal colour vision but be a carrier of the trait. A daughter who inherits the trait from both her mother and her father will be red-green colour blind.
Blue-yellow colour blindness, by contrast, is an autosomal dominant disorder and therefore is not sex-linked and requires only one copy of the defective gene from either parent to be expressed. Achromatopsia is an autosomal recessive disorder, occurring only when two copies of the defective gene (one from each parent) have been inherited. Persons who inherit colour blindness may show symptoms at birth (congenital colour blindness), or they may become symptomatic later, in childhood or adulthood.
Acquired colour blindness is usually of the blue-yellow type and ranges from mild to severe. Often it is associated with chronic disease, such as macular degeneration, glaucoma, diabetes mellitus, retinitis pigmentosa, or Alzheimer disease. Certain drugs and chemicals can also cause acquired colour blindness.