Port 3C0, 00-0F  -  Internal Palette Registers 0 through F

                11xx xxxx  Reserved
                xx1x xxxx  P5
                xxx1 xxxx  P4
                xxxx 1xxx  P3
                xxxx x1xx  P2
                xxxx xx1x  P1
                xxxx xxx1  P0

        Bits 5-0: These 6-bit registers allow a dynamic mapping
                  between the text attribute or graphics color
                  input value and the display color on the CRT
                  screen. When set to 1, this bit selects the
                  apptopriate colot. The Internal Palette registers
                  should be modifyed only during the vertical retrace
                  interval to avoid problems with the displayed image.
                  These interbal palette values are send off-chip to
                  the video DAC, where they serve as addresses into the
                  DAC registers.