WordPress 3.4 “Green,” named in honor of guitarist Grant Green, is ready for you to download right now, and includes a number of new features since last year’s 3.3 release. These new features include “significant improvements to theme customization, custom headers, Twitter embeds and image captions.”

This release follows a recent security update (3.3.2), which resolved a number of pre-existing vulnerabilities. Since then, WordPress has launched version 3 of its iOS app and WordPress.com yesterday added infinite scrolling to its network of hosted blogs.

With WordPress 3.4, the most significant update comes in the form of a new “theme customizer,” which allows admins to change various aspects and settings of a theme in a way similar to Tumblr’s theme editing options. This addition should make WordPress even more accessible for those not interested in diving into the code for theme customization. Of course, theme developers will need to tap into this new feature before it can be used with existing themes, so non-devs should be careful when updating. Update: WordPress just told us that “the new theme customizer works with all existing themes out of the box. Themes can extend the customizer to add additional options and improve the user experience.”

More on that:

Several sections of the customizer will work with all themes — like changing the site title and tagline and specifying a static front page. Other sections are enabled when a theme uses other older WordPress features, like navigation menus, custom backgrounds, and custom headers.

Screen Shot 2012 06 13 at 4.36.19 PM 520x256 WordPress 3.4 is out, featuring better theme customization, Twitter embeds and image captions

The details, from WordPress creator Matt Mullenweg:

The biggest change in 3.4 is the theme customizer which allows you to play around with various looks and settings for your current theme or one you’re thinking about switching to without publishing those changes to the whole world. For themes that support it, you can change colors, backgrounds, and of course custom image headers. We have more planned for the customizer down the road.

Also, enjoy this lovely demo video:

With this new release, users should also expect improvements to custom headers, tweet embed support and HTML image captions. For more, download the latest release and check out the official announcement here.