After the recent release of one of the Google’s major project so called Google Plus (Google +) it seems that google is now engaged to makeover all its services to a new stylish and simple look. Similar to that this simple looking Google themes is now available to your Gmail accounts, however the new interface is not enabled by default to the users account you have to manually apply them. Follow the the process below to grab the new gmail themes.
Changing To New Google Interface
Step 1: Sign-in to your Gmail account and hit Settings icon at top right corner then Mail Settings.
Step 2: Under Mail Settings now click Themes tab, at the end of themes lies two latest themes called Preview and Preview (dense) themes.
The difference is not much alike with the names Preview or Preview (dense), as its just a style of spacing you Gmail interface. The Preview dense theme shows the interface in more compact format with less vertical spacing between emails.
Preview Dense Theme Interface
Below image is the Preview look, having more vertical spaces between emails. Both of the new interfaces are simple, stylish and much cleaner I think the color combination is also good, one of the best themes Gmail ever had.
Preview Theme Interface