I received this question today from Quora. My answer:
The experience of color is part of our sensory system – it is a subset of vision. We experience colors not unlike the way we experience sounds, smells, and tastes – in our brains.
Air doesn’t have color. But, also, bananas and avocados don’t have any color, either. We experience them as being colorful because of the light rays that bounce off them and strike our eyes. Color happens within us – it is not a property of objects.
We see bananas as yellow because their absorb most of the bluish wavelengths of light and strongly reflect most of the yellowish wavelengths. So, somewhat paradoxically, the “signature” color of bananas, which we associate so strongly with them, is caused by the wavelengths that are REJECTED.
Air doesn’t typically have a signature color because it typically doesn’t carry any solid particles for light to selectively bounce off.