In physics, there is no such colour as white. Rather it is a mixture of all the seven colours namely violet, indigo, blue, green, yellow, orange, and red.

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Most people can see about 10 million colours, including 1000 levels of light-dark, 100 levels of yellow-blue, and another 100 levels of red-green.

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The condition chromophobia means a fear or aversion to certain colours. Sufferers can find certain colours upsetting, with erythrophobia, a fear of red, the most common form of the condition, or porphyrophobia, the fear of purple. 

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Mars’ surface is covered in iron oxide, the same substance that makes human blood red.

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If you’ve ever taken the time to think about it, you’ve probably discovered that when you close your eyes, you do not immediately see pitch black. The human eye must transition from light to complete darkness, and the “gray area” you see at such times has a name: eigengrau.

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