I do not have Tk::Pod::Text installed and am not inclined to do so just to test this, but...

Looking at the source of Tk::Pod, I notice:

    -background => ['PASSIVE'], # XXX see comment in Tk::More
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Hmmmm.

In the source of Tk::More there is the line:

    -background => ['PASSIVE'],# XXX ignore -background, so optionAdd 
+works.... still decide
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Looks like you need to set the background color in the option database if you want to have it non-standard in a Tk::Pod::Text object. See perldoc Tk::option.