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.
John Daltons original hypothesis for his deuteranopia was actually that the vitreous humor of his eye was discolored:

I was led to conjecture that one of the humours of my eye must be a transparent, but coloured, medium, so constituted as to absorb red and green rays principally... I suppose it must be the vitreous humor. An autopsy of his eye after his death in 1844 showed this to be definitively untrue, though other filters are possible. Actual physiological examples usually affect the blue-yellow opponent channel and are named Cyanopsia and Xanthopsia, and are most typically an effect of yellowing or removal of the lens. Tetrachromacy in carriers of CVD
Females that are heterozygous for anomalous trichromacy (i.e. carriers) may be tetrachromats. These females have two alleles for either the OPN1MW or OPN1LW gene, and therefore express both the normal and anomalous opsins. Because one X chromosome is inactivated at random in each photoreceptor cell during a females development, those normal and anomalous opsins will be segregated into their own cone cells, and because these cells have different spectral sensitivity, they can functionally operate as different opsins. This theoretical female would therefore have cones with peak sensitivities at 420nm (S cone), 530nm (M cone), 560nm (L cone) and the fourth (anomalous) cone between 530nm and 560nm (either M* or L* cone).If a female is heterozygous for both protanomaly and deuteranomaly, she could be pentachromatic.