I'm starting this thread to so people wanting to create or learn how to customize a color style can ask questions and get help. Everyone is free to contribute.
First Step
Download Firebug for Firefox This is a MUST! Here is an Introduction of what Firebug is: Learn Firebug
Second Step - Decide
Does your project just require customizing the css, to customize the color scheme.
Or
Do you need to edit the Source Image files to customize the look/color scheme.
The majority of your editing will be done in your css files. If you are editing your source files, it's just a matter of saving the slices as the proper image names and uploading them to the proper directory on your server.
The great thing about Firebug is 1. you can find what css file an element is that you need to edit and 2. you can make the changes live in your browser to see what it will look like, then make the changes to the css files.
Now this is just some information to get you started - feel free to ask how-to questions.