Five new themes have now been been added to Gmail:
In Gmail settings, select the ‘Themes’ tab to view and select the new themes.
Note: Themes are only available in Internet Explorer 7.0+, Firefox 2.0+ or Safari 3.0+, and Google Chrome. You won’t see a ‘Themes’ tab in your Settings if you’re not using the newer version of Gmail on the browsers listed above. Please note that Themes are not available if you’re using Internet Explorer 6.0