Gmail owners, Google, wanted "to go beyond simple color customization" and have announced 30 new themes.
There's many new themes to fit your style, a shiny theme with chrome styling, another one that turns your inbox into a retro notepad, nature themes that change scenery over time and even a weather theme that can rain on your mailbox. There's even an old school ascii theme (Terminal) to geek up your mailbox.
Google have also done some work to Gmail's default look to make it "crisper and cleaner".
To customise your inbox, go to the Themes tab under Settings. Google say they will be rolling out themes to everyone over the next couple of days, so you may not see the themes just yet.
Gmail users have been building up custom themes using third-party tools like Greasemonkey or custom user stylesheets for quite some time. Officially, Gmail previously offered the mobile, classic HTML or their normal views only. Google also uses themes in products like their personalised homepage iGoogle or Google Reader's shared items page. The new Gmail themes will certainly be a welcomed addition for many.
Here's an overview of some of the themes to give you an idea of just how far you can customise your Gmail look.