Forge is the new Halo in game editor that runs on PC and XBOX.
To back the stage background black, I edited
C:\Program Files\GIMP 2\share\gimp\2.0\themes\Dark\gtkrc.
color["clrA"] = "#303030" color["clrB"] = "#000000" fg[NORMAL] = @clr2 fg[PRELIGHT] = @clr2 fg[ACTIVE] = @clr3 fg[SELECTED] = @clr1 fg[INSENSITIVE] = @clr3 bg[NORMAL] = @clrB
Here are a bunch of macros for switching from things like RGB to YUV.