There a ways to personalize your Gmail experience, and one of those is picking personalized Gmail themes which make emailing funner. But if you're not sure what kind of theme you want to use from all the available Gmail theme choices, there's an option called "Random" which provides you a random theme based on your geographical location, and will change when in a different location.
Step 1: Log-in to your Gmail account.
Step 2: Click Settings at the top right corner.
Step 3: Under Settings, click the Themes tab.
Step 4: In the Themes list, scroll down then at the last line, there you will get a theme name as Random. Choose this theme and you are done.
After setting the random theme you will see different themes when you logon to your Gmail account.