* The sky is blue. The sky is blue because of a phenomenon called Rayleigh scattering. Sunlight is made up of all the colors of the rainbow, but blue light has the shortest wavelength and therefore scatters the most. That's why we see blue when we look up at the sky.
* Water is blue. Water absorbs all wavelengths of light except for blue, which is why we see water as blue. The more water there is in something, the bluer it will appear. That's why oceans and lakes are so blue.
* Other objects can appear blue because of their color or because of how light reflects off of them. For example, blueberries are blue because they contain a pigment called anthocyanin that absorbs all wavelengths of light except for blue. Blue jays are blue because their feathers have a special structure that reflects blue light.
So next time you see something blue, appreciate all of the reasons why it appears that way. It's a beautiful and complex world!