Some info for you, possibly even useful.
There are a bunch of .tga file in the Resources folder. Some of them may be relevant, and are mentioned below. The relevant ones for the main menu are likely to define the shape of the buttons and the texture of them, but not the color.
The theme files (.thm extension) down under Resource/Theme control, at least mostly, which of the .tga file are used for what purpose.
One of the two important ones for this is the file Civ4Theme_Common.thm. In that file there are color definitions for things. One that may be very useful for you is this one:
Code:
GColor .BG = GColor(117, 82, 44,217) : GFC_Control_Color; //Set for dynamic color change
That is the line from FFH. In regular Bts it uses "GColor( 69, 93,156,217)". If you enter those values into a color choser, like in Paint, you can see that the FFH one is brown and the BtS one is blue. It doesn't look exactly like the colors I expect, so the blending with the tga files presumably has an effect.
The 4 numbers are the values for red, green, blue, and alpha (opacity, lower it to make it more transparent). Note that this same value is used in some other places too.
That definition is referred to as "SF_CtrlTheme_Civ4_Control_Color_BG" in the places where it is used (the ".BG" one the line is appened to the "SF_CtrlTheme_Civ4_Control_Color" in the earlier line that reads "with SF_CtrlTheme_Civ4_Control_Color" but becomes "_BG" for no known reason - whoever invented the theme file format was not big on consistency: things are dfined using "." but used using "_" to separate the parts).
The other theme file that is used for this is Civ4Theme_Custom.thm. In that file is a section that starts like so:
Code:
//Main menu selections panel (Blue main panel)
style SF_CtrlTheme_Civ4_Control_Panel_Main_Style
In there you can see that it mentions "Civ4/Custom/main_menu01.tga". That fodler is under the Resources folder.
The next section after that starts like
Code:
//Main start menu panel (Blue start menu panel)
style SF_CtrlTheme_Civ4_Control_Panel_MainStart_Style
This one mentiones "Civ4/Custom/main_start.tga".
Those define the shapes of things, and possibly affect the transparency.