There are two kinds of colors visible to the human eye: first, visible light; second, invisible light.
The ultraviolet sterilizers used in cafeterias did not actually emit purple light. They emitted visible light so people would know they were working, lest someone see that they were not lit up and give them a couple of slaps.
Even if it really broke down, as long as people could still see the sterilizer giving off "purple light," they would not suspect it had stopped working.
Vision was humanity's primary source of information. What was someone who had always been able to see supposed to do if they suddenly went blind?
Legend had it that Poseidon had a son named Orion. He was a born hunter, yet he did not like living in the water. Poseidon loved this son dearly and gave Orion a miraculous ability: he could walk over the sea as swiftly as flying. But Orion was too arrogant. He boasted that no creature in the world could stand against him, so Hera sent a venomous scorpion to ambush him, poisoning him to death. Once Hera saw that Scorpio had completed its mission, she raised it into the heavens to become the constellation Scorpio.
If a hunter lost his vision, how was he supposed to hunt?
Scorpions had eight eyes: one pair on their backs and three pairs of lateral eyes on either side of their heads. Yet despite having so many eyes, their eyesight was terrible, making them essentially blind. Even with their eyes covered, however, they could still attack prey with precision.
In truth, that experiment had been entirely unnecessary, because scorpions themselves lived in darkness. Ultraviolet light appeared along with sunlight and moonlight. Like Scorpio and Orion, which never met, it was not until humans invented ultraviolet lamps