Question

why there is white colour of sky at noon

Answer 1

Because the suns rays fall directly

Answer 2

    At noon, the sun is overhead in the sky and the light coming from the sun travels a relatively shorter distance through the atmosphere to reach the earth. In this case, the blue light is not scattered much. As the light coming from the overhead sun contains almost all its component colors in the right proportion, the sun appears white to us at noon.       

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