If emplode behaves the way I think it does, then the player you've connected to has it's own window inside emplode. This means that changing the color of the item "Window" in the Appearance tab of Display Properties will not change that white background to something else. Instead, the initial background you see before you connect to a player, when the dialog box is searching, is the color that would be changed.

Of course, not having a copy of emplode on this machine here at work means I could totally be pulling this from between my toes.

Edit: BTW, the Window property doesn't have a foreground and background color, just color for the window (default white) and color for the text displayed in the window (default black).