Definition of colour weakness
The perception of colours is based on the ability to distinguish the three primary colours red, green and blue. All other colours are mixed together from these basic colours. Special light-sensitive cells are responsible for colour vision: the cones, which are located in the retina. If the perception of one of these basic colours is limited, this is called colour vision deficiency, for example red-green vision deficiency and green-blue vision deficiency. In the worst case, if you can no longer see one or more colours at all, this is called colour blindness.
Men and colour weakness
The following figures show how many people are colour blind: About eight percent of all men, but only about 0.4 percent of women suffer from it, reports the Professional Association of Ophthalmologists (BVA). Red-green deficiency is the most widespread, accounting for about 50 percent of all cases. So in Germany alone, about 3.5 million people are affected. Total colour blindness, in which those affected can only distinguish light from dark, is much rarer - only one in 100,000 people suffer from it. In addition, their visual acuity is reduced and they suffer from severe glare .
The following pictures simulate how colour-blind people see the world. The original image is shown as well as its change in the case of red, green or blue blindness:
Figure 1: Simulation of different colour blindnesses. Original (top left), red blindness (top right), green blindness (bottom left) and blue blindness (bottom right).
Possible problems with the operation of a website
It becomes difficult for people with colour vision deficiency when a certain meaning is associated with a colour. Due to colour vision deficiency, differences between different colours can become blurred, making it more difficult to distinguish between them. This can be, for example, the colours of different data in a chart. The problems people encounter here are shown in Figure 2:
Figure 2: On the left the unchanged diagram, on the right with simulated green blindness.
While all colours are easily distinguishable in the left unaltered image, the difference becomes much more difficult for a person with green blindness. The meaning of the colour of buttons, the marking of areas on maps or general coloured areas can also remain hidden to people with colour deficiency.
How Eye-Able adjusts the colors
To help people with color weakness, Eye-Able has integrated the color weakness function. As shown so far, there are different types and degrees of color weakness. Therefore, a total of six different modes are available in Eye-Able . For each color weakness there is a specially adapted procedure, the possibility to remove the colors completely and to increase contrast or color saturation. The intensity can be adjusted for each of the functions. 100% means a correction for color blindness, while smaller values compensate for color weakness. In order to make color differences more visible again for those affected, the affected color areas are shifted towards visible colors. For example, when correcting a red deficiency, the red colors are shifted to the blue color spectrum. Eye-Able adjusts all visible colors on the website. The following figure shows the benefit of this function:
Figure 3: Illustration of colour correction using Ishihara test images (Source: Wellcome collection CC BY 4.0)
As can be seen in Figure 3, color differences can be better displayed again for those affected by color correction. In addition to the respective color weakness modes, increasing the contrast or the color saturation can also lead to an improvement. Another example of how the Eye-Able color correction can make color differences visible again is shown in the following traffic light:
Figure 4: Traffic light with normal colors (left), traffic light for people with red deficiency (middle), traffic light for people with red deficiency after the Eye-Able correction (right)
Sources and further reading
For those interested, here are some of our sources and further information material:
Here you can also carry out an eye test yourself. Caution: An online eye test can therefore only ever provide an indication. If you suspect a colour vision deficiency, please consult an ophthalmologist.
 Françoise Viénot, Hans Brettel and John D. Mollon
Digital video colourmaps for checking the legibility of displays by dichromats
Color Research and Application, 24(4): 243-252, 1999.