The background color for the Joomla! beez template can be changed by editing the position.css file (the purple color)

To find this file, in the backend administrator panel head to:

1. Extensions -> Template Manager
2. In the Template Manager, select from the list the "beez" template and click to edit.
3. Now, click on the "Edit CSS" icon from the right panel.
4. From the list with css files select the position.css and edit it.
   
5. At the beginning of the css file you will find the css property that needs to be modified:

    body
   { background: #F2E3ED;
   color: #000000; font-family: arial, helvetica, sans-serif; font-size: 100.1%; padding: 0px;
   text-align: center;
   }

6. Just replace the background property: background: #F2E3ED with other color.
   For example, if you want a white background for the beez template use:  
   

   background: #FFFFFF;