The CSS rules for things like the menu colours and so on are in the theme’s style.css file (i.e. its style sheet). If you can say what colours exactly you want to change we can probably help, but you’ll possibly void your warranty with the developers if you make changes to their code.
That’s why I’d always go for an Open Source solution, personally.
Also, please bear in mind that although it’s easy enough to see where basic changes like this should be made, if you wanted anything more radical it would not be possible for us to help because we can’t see the code like we can with any of the thousands of open source templates.
You can access your theme’s style sheet from your site’s Dashboard as follows:
Dashboard –> Appearance –> Edit –> Stylesheet
When you have it open in the editor, you can make your changes.
HTH
PAE