However, there is a claim that there is no firm evidence that color deficiency did cause the collision, or that it might have not been the sole cause.In 1920, Frederick William Edridge-Green devised an alternative theory of color vision and color blindness based on Newtons classification of 7 fundamental colors (ROYGBIV). Edridge-Green classified color vision based on how many distinct colors a subject could see in the spectrum. Normal subjects were termed hexachromic as they could not discern Indigo. Subjects with superior color vision, who could discern indigo, where heptachromic. The colorblind were therefore dichromic (equivalent to dichromacy) or tri-, tetra- or pentachromic (anomalous trichromacy). Society and culture
Design implications
Color codes are useful tools for designers to convey information. The interpretation of this information requires users to perform a variety of Color Tasks, usually comparative but also sometimes connotative or denotative. However, these tasks are often problematic for the colorblind when design of the color code has not followed best practices for accessibility. For example, one of the most ubiquitous connotative color codes is the "red means bad and green means good" or similar systems, based on the classic signal light colors. However, this color coding will almost always be undifferentiable to either (Deutans or Protans) and therefore should be avoided or supplemented with a parallel connotative system (symbols, smileys, etc.). Good practices to ensure design is accessible to the colorblind, include:

When possible (e.g. in simple video games or apps), allowing the user to choose their own colors is the most inclusive design practice.
Using other signals that are parallel to the color coding, such as patterns, shapes, size or order. This not only helps color blind people, but also aids understanding by normally sighted people by providing them with multiple reinforcing cues. Using brightness contrast (different shades) in addition to color contrast (different hues)
To achieve good contrast, conventional wisdom suggests converting a (digital) design to grayscale to ensure there is sufficient brightness contrast between colors. However, this does not account for the different perceptions of brightness to different varieties of colorblindness, especially Protans, Tritans and Monochromats. Viewing the design through a CVD Simulator to ensure the information carried by color is still sufficiently conveyed. At a minimum, the design should be visible for Deutans, the most common kind of colorblindness. Maximizing the area of colors (e.g. increase size, thickness or boldness of colored element) makes the color easier to identify. Color contrast improves as the angle the color subtends on the retina increases. This applies to all types of color vision. Maximizing brightness (value) and saturation (chroma) of the colors to maximize color contrast. Converting connotative tasks to comparative tasks by including a legend, even when the meaning is considered obvious (e.g. red means danger). Avoiding denotative color tasks (color naming) when possible. Some denotative tasks can be converted to comparative tasks by depicting the actual color whenever the color name is mentioned; for example, colored typography in "purple", or "purple (█)". For denotative tasks (color naming), using the most common shades of colors.