These kinds of setting should be controlled through the window display options in the Windows Control Panel. Under:
Control Panel>Appearance and Personalization>Personalization>Window Color and Appearance>Advanced settings
you can change the 'Window' colour (and others) to something more to your liking and this will apply to all programs.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]

Thanks, Paul. But that's not the window I'm trying to change. This is the background panel within the Word 2013 program itself. Up top is the ribbon, down the left side is Navigation, then there's the "background" in the palest of grays, and then there's the document itself, which is bright white.