Set color palette

        (EGA) CGA-compatible modes

        Entry:
          AH = 0Bh
          BH = palette color ID
          BL = color to be used with color ID
          (EGA) (graphics modes)
               if BH == 0, BL contains background and border colors (0-15)
               if BH == 1, BL contains palette being selected (0-1)
                         (text modes)
               if BH == 0, BL contains border color (0-15) only
                         (EGA) BL contains border color (0-15) and
                         high-intensity background color (16-31)