SUNSET

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The colour of the beam changes from blue-white to yellow-orange along the length of the beam inside the plastic box containing water with few drops of milk. The same phenomenon is visible inside a glue stick: the end of the glue stick nearest the torch appears white-blue and the opposite end is orange.

This is what happens to the sky, that is blue during the day (when the sun light travels a shorter distance through the atmosphere) and red at the sunset (when the distance travelled is longer).