Moodle has a powerful themes system that provides a variety of visual effects through the use of XHTML and CSS. It has been significantly developed in the more recent versions of Moodle. It is increasingly possible to define your own themes through a knowledge of CSS without knowledge of PHP.
The starting point for any new developer is the standard themes supplied with Moodle. For more options visit the database of available Moodle themes at http://moodle.org/. These may be downloaded and used in your own installation in three steps.
1. Download and extract the .zip file to an empty local directory.
2. Upload the folder to your web server as a subfolder of the /moodle/theme/ folder using the name of the theme you have downloaded as the name of the subfolder. You will need to ensure that the new theme folder and its contents are readable by the web server by ensuring that the Read and Write permissions for the files and folder are set to 755 - Owner read/write/execute, Group read/execute, Everyone read/execute. If the incorrect permissions are set incorrectly, this may prevent display of the newly installed theme.
3. Choose your new theme from within Moodle via Administration > Appearance > Themes > Theme selector.