The sun looks red when it is near the horizon since more light than light has been removed and the light travels through atmosphere when the sun is near the horizon.

blue, red, more                  

Explanation:

At the horizons, during the sunset or sunrise, all the lights gets scattered except red light. Red light has a longer wavelength than the blue light. So from the horizon we are able to see red light or the sun appears red as the wavelength of red light is longer. Other light gets scattered in the atmosphere due to various densities.

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