nGetBackRGB()    Returns the RGB value of the Back color of a byte color
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   nGetBackRGB( <nByteColor> )  -->  <nRGBBack>

   Returns the RGB representation of the back color of one byte color
   format.

   <nByteColor>        Number (One byte) in MsDos color format.

   <nRGBBack>          Number (One long: four bytes) in Windows RGB color
                       format built from the back component of the
                       nByteColor.


   Example:  ? nGetBackRGB( nColorToN( "W+/B" ) )        // WHITE / BLUE
                                  ---> RGB( 0, 0, 128 )  // Blue color