I found the same problem and it was nothing to do with your OSX Appearance settings (ie: Graphite/Aqua). As fas as I can tell it's a bug in the Flashlight interface in Leopard.
My solution was to customize the colours settings in Quicksilver.Go into the QS Preferences, choose 'Appearance' and change the 'Headers' colour field to a blue like in the Spotlight search bar. But this then causes lots of blue elsewhere in QS windows. So it's not perfect. But better than grey IMO. If anyone has a better solution I'd love to know. Pls share :-)
