Compatibility: VGA
Expects: AX    1008H
                                                                  
Returns: BH    current rgbRGB value of the overscan/border register
                                                                  
Info: This obtains the current value of rgbRGB of the VGA overscan
(border) register.  See INT 10H 1000H and EGA I/O Ports for info
on rgbRGB palette register settings.

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INT 10H 1008H: Read Overscan Register