Color blindness, or color deficiency, is caused by genetic mutations or damage to cells at the back of the eye. These cells are responsible for our color vision.
Most individuals who are colorblind are unable to see one of the three colors that the human eye can distinguish: blue, green, and red.
In fact, no two people perceive a particular color the same way. That's because color vision is a complex interplay between photoreceptors, the optic nerve, and the brain.
The optical illusion of color
The visible light that we can see is a type of electromagnetic radiation. Human eyes have the ability to see light waves ranging from 420 nanometers, which is blue, to 680 nanometers, which is red.
The cells responsible for color vision are called cone cells and sit at the back of the eye, in the retina. Each cone cell has one type of color photoreceptor that can pick up blue, green, or red light.
When light enters the eye, the photoreceptors on the cone cells are stimulated and pass messages to the brain via the optic nerve. The combination of input from all three photoreceptors allows us to see complex colors.
The many shades of color blindness
Color deficiency mostly affects men because the genes that are responsible for the green and red photoreceptors are located on the X chromosome.
A man who has inherited one mutated copy of one of these genes will, therefore, be colorblind, as men only have one X chromosome. But women have two copies of this chromosome, and the chance of inheriting a non-mutated photoreceptor gene is subsequently greater.
Color blindness also varies with race. A population study of preschool children identified the rates of color blindness to be highest among non-Hispanic males and lowest among black males.
Red-green color blindness affects around 1 in 12 men of Northern European heritage. This group includes those with any mutations in the red photoreceptor gene (causing protanopia) or the green one (causing deuteranopia).
Blue-yellow color blindness, or tritanopia, is rare and affects both men and women equally. Complete color blindness is very rare, and those who experience it often have other problems with their eyesight in addition to lack of color vision.
There are no treatments for color blindness, but experimental gene therapy has been shown to work in animal models.
'Stop asking me what color things are'
Struggling to pick ripe fruit or chose matching colors for an outfit might be more important to some than others. Yet colorblind individuals can face real challenges in their lives.
Children may struggle to follow colored signposts around their school. And for those who play sports, it can be difficult to distinguish teammates from the opposition.
Likewise, adults often encounter color-coded data, such as graphs and charts, in their professional lives. And certain jobs, such as pilots and safety staff on railways, exclude colorblind individuals. For some, this may mean being unable to take up their dream profession.
Medical News Today spoke with Matt Earwaker, from Brighton in the United Kingdom. He is red-green colorblind. He told us the practical advice that he gives his friends: "Stop asking me what color things are."
"The only real issue I have is with similar colors on board games, so let me use the obviously different colors, like white," he added.
Chances are high that you know someone who is colorblind. Steering clear of reds and greens is a good place to start, but any color that contains red or green elements may be confusing. Better still, let them pick the color of pencils, data charts, or players on a board game, and remember for next time.
And whatever you do, don't keep asking them to tell you what color things are!