How to Change Your Gmail Theme
By default, Gmail is an easily viewable gray, white, black, red and blue. It's professional and easy to look at, but for a web page you'll have open all day, you might want to have a theme that's a bit more personal.
Gmail has a sizable library of themes, or you can add your own. Here's how to change your Gmail theme.
1. Click the Settings cog in the upper-right corner.
2. Choose "Themes" in the drop down.
3. Choose a pre-set image from Google's gallery, to preview, and click save.
4. Alternatively, click "My Photos" to upload your own picture or add a URL for a photo, which will automatically make it your background.
5. Your new background will be set.