GetSysColorBrush constant for background color of a tab control?

Question

I'm using the following APIs to draw a small stock icon on the background of my tab control window (with class name SysTabControl32):

DrawIconEx(hDC, rcIcon.left, rcIcon.top,
    hIconSmInfo, rcIcon.Width(), rcIcon.Height(), NULL, 
    ::GetSysColorBrush(COLOR_WINDOW),
    DI_NORMAL);

But it doesn't seem to draw consistent background. Let me show.

On a themed Windows 7:

It draws it correctly:

But if I remove themes:

It draws this white background:

So what constant do I need to use for GetSysColorBrush?