Hello... so in order to change the colors you need a little skills in css.
First of all login to the admin panel, go to templates, choose your theme template and then choose Css (it is placed on the left) there you will find all the css that are used in your site. Depending on which page you want to change go to the corresponding css, or otherwise the most of them are set in the screen.css
BUT follow my advice if you do not know anything about css do not touch these pages. The css defines how to display the HTML elements. So be careful