That's actually not a border on the info page. It's the border that's placed around all of the modal windows. Since they're shown on a black background, it defaults to white, so the modal windows don't "bleed" into the background. It's hard-coded, and virtually inaccessible via CSS.

The way Floatbox handles the border and "close X" colors is very convoluted. For example, the "close X" color, including the circle around it, isn't controlled by the border color - it's actually controlled by the text color. And the background of that "close X" is controlled by the color of the expander box, not by the color of the body of the info page. Quite a minefield.

To tame it fully, I'd have to add another entire settings panel to the skin's UI, which I'm loath to do. And remember, it all has to work with a bunch of preset styles.