Compatibility: VGA
Expects: AX    1007H
BL    palette register to read (00H-0fH)
Returns: BH    current rgbRGB value of specified register
Info: This obtains the current value of rgbRGB of the specified VGA
palette register.  See INT 10H 1000H and EGA I/O Ports for info
on rgbRGB palette register settings.

Notes: BIOS does not check the validity of BL on this fn and will return
any of the ATC registers (00H-14H).  See EGA I/O Ports.

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INT 10H 1007H: Read One Palette Register