We see blue, because the atmosphere of the Earth scatters the blue light from the sun more than it does for the red light. The scattering causes the blue light particles to cover the sky up more than the red particles. But this changes when sunset and sunrise happens. The angle of which the sunlight hits the atmosphere also affects the scattering. Because the light is cose to a 90 degree angle, the scattering is different at this point than other times.
