Blue is a color, one of the three primary colors of red, green and blue. In the visible light of electromagnetic wave, its frequency is high, the frequency is 600-700 Hz, which belongs to high frequency light.
It is the coldest of the cool colors, and usually reminds people of the ocean, sky, lake and universe, showing a kind of beauty, dreaminess, calmness, reason, tranquility and vastness. In addition, blue also represents melancholy, and this image is also used in literary works.