The blue color of the sky is due to:

The blue color of the sky is primarily due to a phenomenon called scattering, specifically Rayleigh scattering. As sunlight, which is white light composed of all colors, enters Earth's atmosphere, it encounters tiny gas molecules like nitrogen and oxygen. Shorter wavelengths of light, such as blue and violet, are scattered much more efficiently in all directions by these small particles than longer wavelengths, like red and yellow. Because blue light is scattered significantly more, it appears to come from all parts of the sky, making it look blue to our eyes.

• Spread of light is a general term and not the specific physical process responsible for the sky's color.
• Reflection is when light bounces off a surface, which does not explain the overall blue appearance of the sky.
• Refraction is the bending of light as it passes from one medium to another, causing phenomena like rainbows or mirages, but not the general blue color of the sky.