Color blindness or color blindness is most often hereditary and much less often acquired human vision disorder, which causes a huge number of problems. A decrease or complete loss of the ability to distinguish colors seriously interferes with a person in everyday life. There is nothing surprising in the fact that in the first third of the 20th century, people with color blindness were tried not to join the US army. However, the situation changed dramatically in 1941 after America's entry into World War II.
For the draft board (and in the United States at the time of the Second World War, the army was just a conscript for a period), a person with color blindness is actually equal to a disabled person. This is because color blindness seriously complicates life. Many simple everyday tasks for color blind people are almost torture. In the army, such people would be guaranteed to find themselves in a special position, which is frankly not rational. However, when the Americans had to face the Japanese art of disguise in the Pacific Font, the attitude towards color blind people changed dramatically.
The fact is that the classical methods of masking objects in a snowless area work extremely poorly against people with color blindness. For a better understanding, you should understand how camouflage works. The essence of any camouflage is in color differentiation by “mixing” spots of different colors. For example, red-brown ground and yellow-green foliage can be used to mask an object. A position with a machine gun "decorated" in this way will be extremely difficult for an ordinary person to notice. This is because the created color mosaic "smears" the presence of foreign objects on the ground.
However, color blind people see the world differently. They do not notice the red-green differences in the example of the camouflage described above. Instead, the "traitorous" eyes show the color blind a dark yellowish-brown homogeneous mass, instead of a red-brownish-yellow-green mosaic. As a result, color blind people are much better at seeing suspicious irregularities in the terrain, which turn out to be too light or too dark against the general background. Which is extremely useful when detecting enemy positions.
It is interesting that for the first time the usefulness of color blind people in the United States was thought back in 1940. Then in the magazine "Science Magazine" there was an article by Dean B. Judd, dedicated to camouflage and color blindness. Subsequently, the Americans willingly recruited people with color blindness for the role of reconnaissance pilots, as well as for the role of snipers.
If you want to know even more interesting things, then you should read about why not in the USSR or in the USA did not copy the magnetic mines of the Wehrmacht.