Unlike other parts of Office <g> the Office Picture Manager uses the theme/color settings from Windows. The background color is the
setting you have for 'Window' in the desktop properties when you're in 'Thumbnail view' and then it's own beige for other views.
3rd party apps such as
http://irfanview.com have a background setting of their own.
I don't recall a registry setting offhand that will set just the Office Picture Manager viewer background.
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How to make Office Pictures on black background? thanks>>
--
Bob Buckland ?

MS Office System Products MVP
*Courtesy is not expensive and can pay big dividends*