Why is the color of the sky blue?
The sky appears blue to people on Earth during times of the day other than at sunrise and sunset because of the way the light rays from our sun are affected by our atmosphere. The light from the sun is "white" light; it contains the wavelengths of all colors of light. You can see this yourself if you separate sunlight with a prism--different colors (wavelengths) are bent to different angles based on how long their wavelengths are, and a rainbow of colors can be seen. Something similar happens when sunlight hits our atmosphere. The wavelengths that our eyes interpret as blue are short compared to those for red and green; the shorter wavelength blue is "scattered" more by the components of our atmosphere, and is what our eyes perceive when we are looking more or less straight up to the sky. At sunrise and sunset, we see more of the red wavelengths, as the blue wavelengths are scattered so as to be out of our line of sight. The link I have attached has a drawing at the top that shows the relative angles of how the light is sent to our eyes during the day, and at sunset/sunrise.