This episode of Weather for Kids explains why the sky changes colors throughout the day.
Sunlight travels through the atmosphere each day, passing through many air molecules. As the beam hits the molecule, it will scatter all the visible light. Our eyes read these wavelengths of different light, and we see different colors as a result.
For example, during midday, the sun is traveling through the thinnest part of the atmosphere as it is almost directly overhead. All the colors of light are scattered equally, which makes the sun look white to our eyes.
During the morning and evening, as the sun is rising or setting, the length of the atmosphere becomes longer to the location of our eyes. This causes the red colors to become dominant when you view the sky from the location you are in.
So, why is the sky blue? It is because air molecules scatter the blue light more effectively. This is the wavelength that our eyes read as the color blue, which is the most common color during the day.
Smoke and dust particles are larger than air molecules. They will absorb more light causing less to scatter. This will dim the sky color. This is the reason we see more red and orange with a dusty or smokey sky.
The color of the sky has to do with the length of the atmosphere you are looking through and the angle of the sun. Other particles such as dust or smoke will change the color too.