I apologize, but the theme will only allow you to select from the pre-set colors. To setup your own color is going to be a customization you’ll need to make from your Child theme. You can find PSD source images for all of the skins within your download package from ThemeForest. And then you’d implement your custom images with your own CSS overrides.
For CSS changes, it’s a good idea to use a tool like firebug or Google Chrome’s built-in developer tools to locate them and then put the edits either in your child theme or in the “Custom CSS” option on your theme options page.
Also, here’s a helpful tutorial on how to use Firebug – http://vimeo.com/20917974. The only thing I’d suggest not doing is actually making edits to the theme’s CSS files, as it shows at the end of that video. However, the video serves as a good introduction to Firebug and how it can be used to find what CSS is effecting certain areas of your site without ever digging around in any files.