The blue color of the sky is primarily due to a phenomenon called Rayleigh scattering. Here's a simple explanation:

Sunlight is composed of different colors of light, each with a different wavelength. When sunlight enters the Earth's atmosphere, gases and particles in the atmosphere scatter the shorter wavelengths of light (blue and violet) more effectively than the longer wavelengths (red and yellow).

As a result, the blue light is scattered in all directions, giving the sky its blue appearance. This is why the sky looks blue during the day.

At sunrise or sunset, when the sun is lower on the horizon, the sunlight has to pass through more of the Earth's atmosphere. This causes more scattering of the shorter wavelengths, allowing the longer wavelengths to dominate. As a result, the sky often appears red, orange, or pink during these times.

Simple as that!