The degree to which women who are carriers of either protanomaly or deuteranomaly are demonstrably tetrachromatic and require a mixture of four spectral lights to match an arbitrary light is very variable. Jameson et al. have shown that with appropriate and sufficiently sensitive equipment it can be demonstrated that any female carrier of red–green color blindness (i.e. heterozygous protanomaly, or heterozygous deuteranomaly) is a tetrachromat to a greater or lesser extent. Since the incidence of anomalous trichromacy in males is ~6%, which should equal the incidence of anomalous M opsin or L opsin alleles, it follows that the prevalence of unaffected female carriers of colorblindness (and therefore of potential tetrachromats) is 11.3% (i.e. 94% × 6% × 2), based on the Hardy–Weinberg principle. One such woman has been widely reported to be a true or functional tetrachromat, as she can discriminate colors most other people cant. Diagnosis
There are several color perception tests, or color vision standards that are capable of diagnosing or screening for color blindness. The Ishihara color test, which consists of a series of pictures of colored spots, is the test most often used to detect red–green color deficiencies and most often recognized by the public. However, this can be attributed more to its ease of application, and less to do with its precision. In fact, there are several types of common color perception tests. Most clinical tests are designed to be fast, simple, and effective at identifying broad categories of color blindness.
Food
Colorblindness causes difficulty with the connotative color tasks associated with selecting or preparing food, for example:

Selecting food for ripeness can be difficult. The green-yellow transition of bananas is particularly hard to identify. Detecting bruises, mold or rot on some foods
Determining when meat is done by color
Distinguishing some varietals, such as a Braeburn from a Granny Smith apple
Distinguishing colors associated with artificial flavors (e.g. jelly beans, sports drinks)

Skin color
Changes in skin color due to bruising, sunburn, rashes or even blushing are easily missed by those with red-green colorblindness. These discolorations are often linked to the blood oxygen saturation, which affects skin reflectance. Traffic lights
The colors of traffic lights can be difficult for the red-green colorblind. This includes distinguishing:

red/amber lights from sodium street lamps;
green lights (closer to cyan) from normal white lights. Red from amber lights, especially when there are no positional clues available (see image).The main coping mechanism to overcome these challenges is to memorize the position of lights. The order of the common triplet traffic light is standardized as red-amber-green from top to bottom or left to right. Cases that deviate from this standard are rare. One such case is a traffic light in Tipperary Hill in Syracuse, New York, which is upside-down (green-amber-red top to bottom) due to the sentiments of its Irish American community. However, it has been criticized due to the potential hazard it poses for color-blind drivers. Signal lights
Navigation lights in marine and aviation settings employ red and green lights to signal the relative position of other ships or aircraft.