This question already has an answer here:
Randall Monroe, a credible source in my opinion, says that the sky is blue because the air is:
Normal light interacts with the atmosphere through Rayleigh scattering. You may have heard of Rayleigh scattering as the answer to "why is the sky blue." This is sort of true, but honestly, a better answer to this question might be "because air is blue." Sure, it appears blue for a bunch of physics reasons, but everything appears the color it is for a bunch of physics reasons.
But is the air really blue? Color is created by matter absorbing some wavelengths, while reflecting or transmitting others (as explained, for example, here). Air transmits the entire spectrum equally, but in different directions, which would make it colorless (white?), not blue.
So, is Randall wrong?
To clarify about possible duplicates - I'm asking whether the air, not the sky, is blue. I don't ask about the physical phenomena that make them so - this one was asked and answered.