I have always loved shadows. They add detail and depth to scenes. Depending on how they form, they can create mysteri-ous patterns and often create images themselves. They can alos be used to great effect as a special effect to highlight or focus your attention on an object or character.
One way to use shadows as a special effect is to change their color. I am going to show you a few ways to change the color of shadows.
First you need a scene of course and a lighting set up to play with. I started with a very basic light set up. There are three spot lights:
One spotlight (main spot) set up behind the camera 2 linked spots set to the sides And a little AO for interest While this set up works rather well on it's own, it is alos a great starting point for a little shadow fun.

Fun with Shadows-1.jpg

Using Nodes

I set up my render passes to give me a "Combined and a Shadow pass". Then I opened up the Node Editor and started getting it all set up.
Quik Rundown: Render Layer panel Shows the combined (original) image connec-tions: Connect Image to 1st Image socket on Mix Node Connect Shadow to Image socket on RGB Curve Node 1a, 1b & 2a are Viewer Nodes to show you what each step produces.
RGB Curve Node the RGB curve is used to adjust the color of the Shadow Connect Image to 2nd Image socket of Mix Node. Mix Node Takes the original image and the color corrected shadow image and combines them into a new image.
Okay, time to Render, making sure that "Compositing'' is checked in the 'Post Processing' panel of the Render buttons.

Fun with Shadows-2.jpg

Well the shadows are definitely Blue, but they no longer have that software blended look. Something that ren-dering out and adjusting additional passes (such as AO, Environment and Indirect Lighting) would take care of, in addition to perhaps a blur node
or two for blending.
The fun thing about the above method, is that once you have separated out the shadow pass, you can replace it with a com-pletely different shadow pass to create some cool special effects.
Imagine an everyday character with a monster shaped shadow.
How cool would that be.

Lamp by Lamp

A simpler way to change shadow color is to change it on each lamp in your scene. This resulted in a very nice effect. The shadows cast by the three spots rendered as blue, leaving the AO shadows a nice software gray.

Fun with Shadows-3.jpg

This would be an effective way to bring focus to one or two elements in your image.

Fun with Shadows-4.jpg

Sky & Texture

But what if you wanted all the shad-ows to be blue. Well that is very easy too.
Change your Environment setting from "white" to "sky texture". Change your main spot light to Sun.
In the "Sky & Texture" panel select "Mountain" leaving everything else at default and render.

Fun with Shadows-5.jpg

Now all shadows are various shades of Blue and you still have your software blended shadows. This is just a few ways that shadows can be altered, all of the above methods can be combined and adjusted as needed for what ever you could need.
To ends my shadow fun adventure. I hope enjoyed yourself and learned a thing or two.

Fun with Shadows-6.jpg