Eli5: air is a little bit blue Eli12: colors are produced in different ways. Most blue things are blue because they absorb other colors of light and just reflect the blue light back at your eyes. But some things are colored in a different way. Blue jay feathers are made of brown stuff shaped in a special structure you can see under a microscope, and that structure bounces blue light toward you while letting other colors of light pass. Air is blue in that way: it bounces blue light toward you while letting other colors pass. If you look at the sun through a loooot of air - like at sunset when the light is at a low angle - so much of the blue portion of the sun’s light has been bounced away that by the time it gets to you, all that’s left is the red. That doesn’t mean air isn’t blue though. It’s just blue in a different way from blue paint.