The phenomenon you are referring to is known as Cherenkov radiation. When a charged particle, such as an electron, moves through a medium (like water) at a speed faster than the phase velocity of light in that medium, it emits electromagnetic radiation. This radiation is known as Cherenkov radiation.
In air, the speed of light is also slower than its speed in a vacuum, but the effect is much less pronounced compared to the speed reduction in water. Therefore, for most everyday objects and speeds we encounter in air, Cherenkov radiation does not occur.
However, in certain specialized circumstances, such as in high-energy particle physics experiments or nuclear reactors, where high-speed particles are involved, it is possible to observe Cherenkov radiation in air. In these cases, the Cherenkov radiation would still appear as a faint bluish glow.
The blue color of Cherenkov radiation is due to the fact that the emitted radiation has a characteristic spectrum that is predominantly in the blue to ultraviolet range. The exact color can vary depending on the properties of the medium and the particle's speed.
It's important to note that Cherenkov radiation in air is a relatively rare and specialized phenomenon. In most everyday situations, the speed of light in air is close enough to its speed in a vacuum that the effects on visible light are negligible, and Cherenkov radiation is not observed.