The Setting Sun Isn't Directly Above You Anymore, Right?

As the sun sets, it must take a longer pass to get through the atmosphere and to you on Earth. That means it hits even more gases and particles on its path through the atmosphere. Blue waves are the short, choppy, high energy waves. And they're more likely to hit these particles in the atmosphere and be scattered. So we see different sky colors at different times of day because of where the sun is primarily.