Out of the box, WP-Syntax colors code using the default GeSHi colors. Per the authors advice in the ‘Advanced Customization’ section of Other Notes, you can configure GeSHi yourself by handling the wp_syntax_init_geshi hook and configuring it programmatically.
Since I wanted to do just that, I decided to publish a generic plugin, called wp-syntax-rettke, for folks who wanted to configure GeSHi following this approach.