INT 10 - VIDEO - SET SINGLE PALETTE REGISTER (PCjr,EGA,MCGA,VGA)
        AX = 1000h
        BL = palette register number (00h-0Fh)
           = attribute register number (undocumented)
             10h attribute mode control register (should let BIOS control this)
             11h overscan color register (see also AX=1001h)
             12h color plane enable register (bits 3-0 enable corresponding
                text attribute bit)
             13h horizontal PEL panning register
             14h color select register
        BH = color or attribute register value
Notes:  on MCGA, only BX = 0712h is supported
        under UltraVision, the palette locking status (see AX=CD01h)
          determines the outcome
SeeAlso: AX=1007h,AX=CD01h