Subject: Why does the sky change color with the seasons?

I've noticed that the color of the sky is a slightly different hue in each 
season.  The change for spring and for fall is generally more noticable, as it 
generally happens within a few days, but all four change to some degree.  Since 
the spring and fall changes are linked to weather changes, I've thought that it 
was simply a matter of the consistency of the atmosphere, but I wish to know 
what, specifically, the changes are, and if the angle of the earth plays a role.

Re: Why does the sky change color with the seasons?