Office 2013 users can change the background and theme using the settings available as part of the Word options.Changing the background and themes would be helpful to quickly identify your opened Office 2013 application when you have other application running at the same time.
Change background in Office 2013
Launch any one of the Office 2013 application(Word, Excel, Outlook) then click the File menu followed by Options. In the General Options screen, navigate to Personalize your copy of Microsoft Office section and click the drop down with the label as Office background.
Now you can choose your desired from the list of available backgrounds.
Change themes in Office 2013
Similarly Office 2013 users can change the themes using the Office Theme options available as part of the General Options.
Click the Office Theme drop down and choose White or Light Gray or Dark Gray from the list.
Change scheme in Office 2007
Office 2007 users can use the scheme option to change the Office background and the default colour theme is blue.
This theme can be set using the Word Options.
Under Word Options, Popular menu, you can find Colour scheme under Top options for Working with Word.
The different styles that are available are Blue (default), Silver and Black. This is how Word looks with colour theme as Black.
Also See: Add background color in Word 2013