NAME
       GetRGB4 -- Inquire value of entry in colormap.

   SYNOPSIS
       value = GetRGB4( colormap, entry )
          d0              a0       d0

        ULONG GetRGB4(struct colormap *, long);

   FUNCTION
        read and format a value from the colormap.

   INPUTS
        colormap - pointer to colormap structure
        entry - index into colormap

   RESULT
        returns -1 if no valid entry
        return uword rgb value 4 bits per gun right justified

   NOTE
        Intuition's displaybeep() changes color 0. reading color 0 during a
        displaybeep() will lead to incorrect results.

   BUGS

   SEE ALSO
       setrgb4() loadrgb4() getcolormap() freecolormap() graphics/view.h