I include a section on Color Blindness as it is common, 8 -13%, in men, Therefore it is probably common among beer drinkers! I know several persons who have just discovered their color blindness at a late age. Please see the color blindness test page if curious. Obviously this would affect you ability to evaluate the color of your beers.
The ability of the human eye to distinguish colors is based upon the varying sensitivity of different cells in the retina to light of different wavelengths. The retina contains three types of color receptor cells, or cones. One type, relatively distinct from the other two, is most responsive to light that we perceive as violet, with wavelengths around 420 nm. (Cones of this type are sometimes called short-wavelength cones, S cones, or, misleadingly, blue cones.) The other two types are closely related genetically and chemically. One of them (sometimes called long-wavelength cones, L cones, or, misleadingly, red cones) is most sensitive to light we perceive as yellowish-green, with wavelengths around 564 nm; the other type (sometimes called middle-wavelength cones, M cones, or, misleadingly, green cones) is most sensitive to light perceived as green, with wavelengths around 534 nm.
Light, no matter how complex its composition of wavelengths, is reduced to three color components by the eye. For each location in the visual field, the three types of cones yield three signals based on the extent to which each is stimulated. These values are sometimes called tristimulus values.
The response curve as a function of wavelength for each type of cone is illustrated above. Because the curves overlap, some tristimulus values do not occur for any incoming light combination. For example, it is not possible to stimulate only the mid-wavelength/"green" cones; the other cones will inevitably be stimulated to some degree at the same time. The set of all possible tristimulus values determines the human color space. It has been estimated that humans can distinguish roughly 10 million different colors.
The other type of light-sensitive cell in the eye, the rod, has a different response curve. In normal situations, when light is bright enough to strongly stimulate the cones, rods play virtually no role in vision at all. On the other hand, in dim light, the cones are understimulated leaving only the signal from the rods, resulting in a colorless response.
Color blindness is: Color blindness (color vision deficiency) is a condition in which certain colors cannot be distinguished, and is most commonly due to an inherited condition. Red/Green color blindness is by far the most common form, about 99%, and causes problems in distinguishing reds and greens. Another color deficiency Blue/Yellow also exists, but is rare and there is no commonly available test for it. Total color blindness (seeing in only shades of gray) is extremely rare. There is no treatment for color blindness, nor is it usually the cause of any significant disability. However, it can be very frustrating for individuals affected by it. Those who are not color blind seem to have the misconception that color blindness means that a color blind person sees only in black and white or shades of gray. While this sort of condition is possible, it is extremely rare. Being color blind does keep one from performing certain jobs and makes others difficult.
Regular vision is Trichromatic - it uses all three
color pigments (red/green/blue).
Although defective color vision may be acquired as a result of another eye or brain disorder, the vast majority of color blind cases are hereditary - present at birth. The gene for this is carried in the X chromosome. Since males have an X-Y pairing and females have X-X, color blindness can occur much more easily in males and is typically passed to them by their mothers. Color blindness is rooted in the chromosomal differences between males and females. Females may be carriers of color blindness, but males are more commonly affected.
Color blindness is normally diagnosed through clinical testing. The Ishihara color test the one most common test used Although there is no treatment for color blindness, most color deficient persons compensate well for their defect and may even discover instances in which they can discern details and images that would escape normal-sighted persons. At one time the U.S. Army found that color blind persons can spot "camouflage" colors where those with normal color vision are fooled by it.