Ohhh great question!
When the sun is over head light is scattered by the air in a very particular way (called Rayleigh Scattering) which means some blue light is scattered while all the other colours pass straight through. If we could see in ultraviolet, the sky would actually look purple!
When the sun sets the sun ends up an angle to Earth, this means the blue light is now reflected away from the people on the ground. Red light is also bent towards us because of the atmosphere (called atmospheric refraction). This means we end up with more red light and less blue light!
I’ll add a picture for the sunset scenario, hopefully it will help visualise it 🙂
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Abu.D15 commented on :
thank you