You will need Certified Manager (theme access) to perform this task.

Open the Design/Templates application. In Applications skins, open the Global file.

From there, open the global-core-zen folder. Under then, open the resources folder, then styles and site. After that, double-click the site.css file.

Enter the following code. You can either use a hex code or just enter the name of the color.

#blox-html-container.christmas {

background-color: #006E25; }

 Use the URL you want to target in place of "christmas."