The reason for the reddish sunsets and dawns is Rayleigh scattering. The colors have different wavelengths. For example, blue has a short wavelength, so it isn’t scattered so much. In the mean time, red light has a short wavelength and scatters in the atmosphere when it travels for a while. When the Sun is high, the blue light takes a shorter route through the atmosphere and gives the sky a blue color. When the Sun is lower, the light has to travel through the atmosphere for longer and the blue light is scattered while the red one remains.