I think you already know about QuickSilver and how to change the hotkey. If you haven't know, you can refer back to QuickSilver - Setting Up Your Most Favorite HotKey.

Now go under QuickSilver Preferences and then look for the Appearance tab in the sidebar. There you can see the Command Interface area.

There are some interfaces of QuickSilver you can choose, such as Primer and Bezel. The Primer interface is built-in, so everyone will have this interface. The interface looks like this

Bezel interface is an additional interface. It looks like this

There are also nine buttons to select color for your interface and two check box. You can see where they are located at image above.

Each of these nine buttons specify :

	Primer Interface	Bezel Interface
Bezels
←		Background Color
=		Highlight Color
→		Font Color
Headers
←	Background Color	List Header Color
=	Highlight Color
→	Shadow Color	Shadow Color
Lists
←	List Background Color	List Background Color
=	List Highlight Color	List Highlight Color
→	List Font Color	List Font Color

And two check boxes to disable/enable Glass Effect and Shadow Effect.

That's all for changing interface.