It seems I am not the only programmer wondering which system color the tab control is supposed to match.
http://forums.ni.com/t5/LabVIEW/Dialog-color-that-matches-tab-in-the-XP-theme-too/td-p/122525

I found this comprehensive Windows System Colors Reference 
http://www.quppa.net/syscol/
It shows graphically what each system color looks like across every Windows flavor and theme. It looks like the Window system color is the closest match to the tab control color across Win 7 themes. 

I have made my own version of EV_STOCK_COLORS overriding default_background_color returning the Window system color for Win 7 themes and the precursor for XP or the Classic theme.