The color of the sun is reddish at the time of sunrise and sunset where as at noon the sun appears white. At sunrise and sunset the sun is at the horizon and atmosphere near the horizon is thicker. The light coming from the sun has to travel a longer distance through the atmosphere to reach us. Therefore, sunlight suffers scattering where most of the colors of light get scattered away due to their shorter wavelengths and only red light reaches our eyes because of its high wavelength.
Hence, during sunrise and sunset the sun appears reddish. When the sun is overhead at noon, then the light coming from the sun has to travel a relatively shorter distance through the atmosphere to reach us. Therefore white light doesn't get scattered away.