Hi Latino,
All the colours in your website are controlled by your skin1.css unless you have other add-ons or 3rd party modules, some which have their own css files.
You will also need to grab a copy of Dreamweaver or other WYSIWYG html editor as some of the tables have images called not just colours and these you'll find are primarily in your skin1/images folder. Although you can use notepad or wordpad to edit your tpl files, Dreamweaver makes it just so much easier.
Use Webmaster mode religiously while you are setting up your store, it is a must, as you need to be careful about changing too much on one template which just so happens to connect to another which will in turn screw your whole site upside down. Been there, done that and learnt a hell of a lot on the way.
Also take a look at Balinor's sticky notes regarding template editing it is invaluable as you learn this not so easy cart software. Once you get a handle on it, you can really fly.
http://forum.x-cart.com/showthread.php?t=21529
Have fun
beetlejuice