This function returns the system color.

#define INCL_WINSYS /* Or use INCL_WIN, INCL_PM, */
#include <os2.h>

HWND    hwndDesktop;  /*  Desktop-window handle. */
LONG    clr;          /*  System color-index value. */
LONG    lReserved;    /*  Reserved value, must be 0. */
LONG    lRgbColor;    /*  RGB value. */

lRgbColor = WinQuerySysColor(hwndDesktop,
              clr, lReserved);