I did originally try to set the background as black, but because I used background images the background color becomes mute. I just never removed the code for the color when I upgraded my GUI.
GUICreate($name, 300, 400)
GuiCtrlCreateTab(1, 0, 300, 400)
$background3 = GUICtrlCreatePic("bg/1.jpg", 2, 23, 296, 376)
If you create a folder named bg and have your background image named 1.jpg then 2 and 3 and 4 the images will show up in the tabs. This code is located starting @ line 71 if viewed in the scite editor.
Move this back to the hacks section.