The dark blue sky results from the use of a (circular) polarizing filter.
It worked almost too well in this instance, since it created too much
contrast between the tree trunks and the sky, so I had to lighten
the sky with the Shadows/Highlights tool in Photoshop Elements 5.
Copyright © Wolfgang Bluhm. All Rights Reserved. Please do not reproduce, alter, or use without prior permission of the author.