COLOR BLINDNESS: ¿How many colors do you see?

The 6th of September is International Color Blindness Day.

What is color blindness? DBGen offers a brief explanation of color perception in humans and the associated genetic defects.


Colors are our brain’s interpretation of light signals and it classifies them according to their wavelength. For example, we identify light signals between 380 and 450 nm as violet, while light with a wavelength between 620 and 780 nm is perceived as red. Humans can only see colors between 380 and 780 nm, this range is named the visible spectrum. The human eye, like a printer, detects the colors using only 3 types of cones, photoreceptor cells, capable of capturing light of different wavelengths: S cones (blue), M cones (green) and L cones (red). The light stimuli is converted into nerve impulses that are transmitted to the brain, which will combine and interpret them in order to perceive the different colors. However, if one or more of these types of photoreceptors are absent or dysfunctional, the detection and interpretation of light signals will be affected, and color vision will be impaired: this is the case of dyschromatopsia or color blindness.


Range of wavelengths that excite different types of human cones. Humans have S, M and L cones. The R range corresponds to the excitation of rhodopsin, the pigment of another type of photoreceptor cell in the human eye, the rods, responsible for low light conditions.


There are different types of color blindness depending on the affected photoreceptor:


  • Protanopia/Protanomalopia: Lack/dysfunction of L cones, responsible for the color red, so that reddish colors resemble beige or brown and green can be confused with red.


  • Deuteranopia/Deuteranomalopia: Lack/dysfunction of M cones. It is the most common type of color blindness. Due to the close range detected by the L and M cones, the effects are similar to protanopia, although the reds do not appear as dark.


  • Tritanopia/Tritanomalopia: Lack/dysfunction of S cones. In this case, blue and green are confused and yellow resembles red.


  • Monochromatic color blindness: Only one type of cone is available and vision is reduced to that color range.


  • Achromatopsia: Lack/Dysfunction of all types of cones, resulting in colorless vision. Furthermore, unlike the other cases, it is associated with reduced visual acuity and photophobia, increased sensitivity to light.



Combinación de colores, tal y como las perciben aquellos con deuteranopia, protanopia, tritanopia y acromatopsia
How do those affected by different types of color blindness or achromatopsia perceive color combinations? The combination that allows greater discrimination is violet with orange (image created by Lluís Montoliu, and extracted from his blog GEN-ÉTICA


The clinical diagnosis of these conditions is normally carried out through visual tests in which the proband has to identify a number (Ishihara test) or put colored chips on the correct order discerning between specific colors and slight hue variations within a given color.(Farnsworth test). Genetic testing, generally performed for counseling and family planning, the opsin genes located on the X chromosome are analyzed for mutations. Color blindness is not generally considered a disability, since those affected still have a normal life. Nevertheless, it can be a incapacitating for certain professional activities where color discrimination is crucial, such as pilot, air traffic controller or electrician.


When preparing a class or exhibition, it is important to consider the different needs of the target audience. For this reason, different tools have been proposed from Photoshop filters that help to combine colors that can make life easier for colorblind. The color combination that allows better discrimination for humans, with or without color blindness, is violet with orange.


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