Blue is more commonly associated with sadness, the sky and ocean. In the middle ages it was also associated with the poor.
In several languages there is no distinction between the colors blue and green.
In the United States and Europe blue is the people's favorite color by more than 50%.
The sky and ocean appear blue because blue has the shortest wavelength (of the visible colors) and is thus more scattered by the oxygen and nitrogen in the atmosphere and water.
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