Occupations
Color blindness may make it difficult or impossible for a person to engage in certain occupations. Persons with color blindness may be legally or practically barred from occupations in which color perception is an essential part of the job (e.g., mixing paint colors), or in which color perception is important for safety (e.g., operating vehicles in response to color-coded signals). This occupational safety principle originates from the aftermath of the 1875 Lagerlunda train crash, which Alarik Frithiof Holmgren blamed on the color blindness of the engineer and created the first occupational screening test against the colorblind. ...I consider that to [Holmgren] above all others do we owe the present and future control of color-blindness on land and sea, by which life and property are safer, and the risks of travelling less. Color vision is important for occupations using telephone or computer networking cabling, as the individual wires inside the cables are color-coded using green, orange, brown, blue and white colors. Electronic wiring, transformers, resistors, and capacitors are color-coded as well, using black, brown, red, orange, yellow, green, blue, violet, gray, white, silver, gold. Driving
Red-green colorblindness can make it difficult to drive, primarily due to the inability to differentiate red-amber-green traffic lights. Protans are further disadvantaged due to the darkened perception of reds, which can make it more difficult to quickly recognize brake lights. In response, some countries have refused to grant drivers licenses to individuals with color blindness:

In April 2003, Romania removed color blindness from its list of disqualifying conditions for learner drivers licenses.
Lantern
Instead of the Ishihara test, the US Navy and US Army also allow testing with the a lantern, such as the Farnsworth Lantern Test. Lanterns project small colored lights to a subject, who is required to identify the color of the lights. The colors are those of typical signal lights, i.e. red, green and yellow, which also happen to be colors of confusion of red-green CVD. Lanterns do not diagnose colorblind, but they are occupational screening tests to ensure an applicant has sufficient color discrimination to be able to perform a job. This test allows 30% of color deficient individuals, generally with mild CVD, to pass. Arrangement tests
Arrangement tests can be used as screening or diagnostic tools. The Farnsworth–Munsell 100 hue test is sensitive enough that it not only can detect color blindness, but also evaluate the color vision of color normals, ranking them as low, average or superior. The Farnsworth D-15 is simpler and is used for screening for CVD. In either case, the subject is asked to arrange a set of colored caps or chips to form a gradual transition of color between two anchor caps. Anomaloscope
An instrument called an anomaloscope can also be used for diagnosis. These instruments are very expensive and require expertise to administer, so are generally only used in academic settings. However, they are very precise, being able to diagnose the type and severity of color blindness with high confidence.