INT 10 - VIDEO - READ OVERSCAN (BORDER COLOR) REGISTER (VGA,UltraVision v2+)
        AX = 1008h
Return: BH = border color (00h-3Fh)
Note:   UltraVision v2+ supports this function even on color EGA systems in
          video modes 00h-03h, 10h, and 12h; direct programming of the palette
          registers will cause incorrect results because the EGA registers are
          write-only.  To guard against older versions or unsupported video
          modes, programs which expect to use this function on EGA systems
          should set BH to FFh on entry.