Why is sky blue?

The molecules of gases in our atmosphere scatter sunlight; the color scattered the most without being absorbed is blue - that's what we see. When the sun is down, there's no light to scatter - and we see the atmosphere as it truly is - clear.
The effect is called "Rayleigh scattering."

It is related to scattering of light. There are 7 light band in spectrum. Violet, indigo, blue, green, yellow, orange and red. Red has the least wave length. The blue light due to its short wavelength is scattered more than blue. Hence sky appear blue

Its such a shame kids today can't take a few seconds to search for information online. And can't be bothered to see if some other kids have already asked this exact same question. This is one of the most frequently asked (and answered) question in Astronomy.

http://www.kidsgeo.com/geography-for-kids/0045-why-is-the-sky-blue.php
http://www.whyistheskyblue.co/for-kids.php
http://spaceplace.nasa.gov/blue-sky/en/

Its a sad statement on the education system that doesn't teach science and doesn't teach kids how to learn.

And there's nothing I can do

It's not. It only look sky blue on a sunny day, due to water in the atmosphere.