Themes allow you to control the overall look of Gmail without changing its functionality. Gmail provides a number of default themes, and you can even create your own.
1) To change your theme, go to Settings.
2) Open the Themes tab. The default theme is Bold Blue. As of November 2009, there are 33 other themes for you to choose from.
3) You can also pick a Random theme or Choose your own colors.
4) Let's choose an existing theme... we'll pick the Steel theme.
5) After a moment, your theme will have been changed. Success!
This completes the tutorial. You now know how to change your theme in Gmail.