The latest development version of Google Chrome (version 18.104.22.168 which was a bug fix over 22.214.171.124) has added support for installing themes to the browser, unlike the earlier route of installing themes in Google Chrome.
The newer version also does not require you to enable extensions using the enable-extensions switch, the browser can now automatically handle it.
At present there are two sample themes available Camo and Snowflake which you can try out on the newer version. Downloading and installing themes are easy just download the file and it will change the theme without restarting the browser.
How do you manage themes in Google Chrome? This version includes a basic theme management in Options > Personal Stuff tab, right now you can switch back to default theme or get new themes.
The get new themes points to a non-existent Google Chrome Theme gallery page, however that should not be the case in the future.
The one feature that is missing however is the ability to find and see installed themes, but that too will be fixed in the future.
And in addition to that the new tab page will be available by default now, it also adds support for the well received HTML 5 video tags.