To change the theme for Google Chrome you will need to replace the default.dll file with the new theme file. Location for theme folder are as follows

For Vista Users: C:\Users\UserName\AppData\Local\Google\Chrome\Application\0.2.149.27\Themes\

For XP Users: C:\Documents and Settings\UserName\Local Settings\Application Data\Google\Chrome\Application\0.2.149.27\Themes\

Replace C with your Windows directory, UserName with the user name you have installed chromed with, the number is the version for Google Chrome.

Make sure to keep a backup of the default.dll, before you overwrite it with a new one. DeviantArt already has a Picthblack theme which you can use to replace the default Google Chrome theme.

Other Resources to Download Google Themes

* Chrome Dark

* 3 Themes for Google Chrome