The theme is a set of colors, fonts, and decorative elements that provide a consistent appearance to your site. A site comes with a set of themes that enable you to quickly change the appearance, based on your organization's needs.
Applying a theme does not affect the layout or content of your site. It also does not change the theme of any specific pages that you applied a theme to by using a Web design program that is compatible with Microsoft Windows SharePoint Services, such as Microsoft Office SharePoint Designer 2007.
To change the theme of a site, you must have the Design permission level.
On the Site Actions menu , click Site Settings.
Note: On a site for which the Site Actions menu is customized, point to Site Settings, and then click the settings that you want to view.
Under Look and Feel, click Site theme.
Select the theme that you want.
Note: You can also design and apply custom themes by using a program that is compatible with Windows SharePoint Services. You can also change the colors, fonts, and other formatting without changing the theme by editing the core.css style sheet for a site with a Web design program. For more information, see Help in your Web design program.