Color, contrast, and human perception of them is pretty amazing.
This reminds me of something I was watching last night about the Sun. We've all seen photos of sun-spots right? Those dark spots on the sun indicating increased Coronal mass ejections etc. Those "dark" spots are actually quite bright, in fact, if you could remove one from the sun's surface and float it in black space next to our moon, the "dark" spot would be something like 100 times brighter than the brightest full moon, as observed from earth. The spots only appear "dark" on the sun because of the brightness of the sun itself, and the contrast to the spots.
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"In the event that I am reincarnated, I would like to return as a deadly virus, in order to contribute something to solve overpopulation" Prince Philip 1988