Importing NavigationPaneBackground into a theme that didn't originally have it?

I'm currently using the standard Windows 8 Release Preview theme on a system running Windows 8 (build 9200, not 8.1). The theme works pretty well, but I'd like to have something other than solid white on the Control Panel Task Pane, identified with number 3 on the image below: (yes, I know the screenshot shows a gray background on a Windows 7 system; it's just an example)

https://1.bp.blogspot.com/_hNr0c9uRdz...0/dbulx3xm.jpg

I realize that this would normally require messing around with shell32.dll, but the system in question has OldNewExplorer installed, so it'll make use of all of the Style Builder features without having to mess around with the system files. Specifically, I'm looking at "Explorer & Shell > Explorer > Control Panel > ControlPanel > NavigationPane > NavigationPane Background" and "NavigationPaneTop Background." The trouble is, on the destination theme that I want to add these elements to, I can find no way to import the graphics for these components. Exporting as a Stylehack from the source theme is successful, but trying to import the Stylehack into this one is not. Even more baffling is that if I start over fresh with a blank theme file, the Stylehack does import successfully.

Attachment 78312

Can somebody tell me what I am doing wrong or overlooking with this?