Office 2007's default color is blue; I'll show you here how to change it to silver or black.
EDIT: I recently discovered while writing up this blog post that doing this affects the following Office 2007 windows: Word, Excel, PowerPoint, Outlook, and Access. It does not noticeably affect OneNote, InfoPath, or Publisher. I could not check Groove; I did not want to make an account.
Step 1: Click the Logo
Click on the little Microsoft Office logo in the top left corner of your window.
Step 2: Word Option
Click on Word Options, at the very bottom of the list
Step 3: Drop and Give Me Colors!
Make sure that the window is set to 'Popular' then click on the drop-down list that currently says 'Blue'
Step 4: Pick Your Poison
Choose either silver or black. I prefer black.
Then click OK.
Step 5: Ta-Da!
And thus, you are done. Enjoy your new colorific Office window.