Customize Highlight Bezel of roPosterScreen

I would like to change the bezel that surrounds the selected item on the roPosterScreen. The http://sdkdocs.roku.com/display/sdkdoc/roAppManager documentation has ListItemHighlightHD and ListItemHighlightSD that seem to indicate that you can do this (both of them say they apply to the grid, list, and poster screens. But neither of them seems to do anything to the poster screen.

Note that I'm not using subcategories on the poster screen, so if that's what the ListItemHighlightHD and ListItemHighlightSD variables apply to, that'd explain why I'm not seeing them. I want to change the bezel around the selected item in the center of the screen. I'm using the flat-category list style on roPosterScreen.