The sky appears blue to the human eye because of a phenomenon called Rayleigh scattering. This occurs when light from the sun, which is white in color, enters the Earth's atmosphere and is scattered in all directions by the gases and particles that make up the atmosphere. The blue color is caused by the fact that short-wavelength light (blue and violet) is scattered more than long-wavelength light (red and orange) by the gases and particles in the atmosphere.
Rayleigh scattering is inversely proportional to the fourth power of the wavelength of light. So, blue light with a wavelength of about 475 nanometers is scattered about 10 times more than red light with a wavelength of about 650 nanometers. This means that blue light is much more likely to be scattered in all directions, making it more visible to us from all angles. That's why the sky appears blue to us during the day when the sun is high in the sky, and the light from the sun has to travel through more of the Earth's atmosphere before it reaches our eyes.
It's worth noting that the sky can appear in different colors during different times of the day or under different atmospheric conditions. For example, during sunrise or sunset, the sun's light has to travel through more of the Earth's atmosphere which causes more scattering, making the sky appear red, orange, or pink. Similarly, the sky can appear gray or white during overcast days when clouds block the sun's light from reaching the ground.