xBase MsDos color management
 --------------------------------------------------------------------------------

 Standard MsDos xBase color management is based on strings which are a
 combination of the following elements:

           Base colors

       Black ......... "N"                   Color structure
       Blue  ......... "B"
       Green ......... "G"         [ + ] [ * ] "<ForeColor> / <BackColor>"
       Cyan  ......... "BG"
       Red   ......... "R"
       Magenta ....... "RB"
       Brown ......... "GR"  (a/k/a yellow)
       White ......... "W"


  [ + ]             Intensity
  [ * ]             Blinking  or Back intensity
  <ForeColor>       One of the above base colors
  <BackColor>       One of the above base colors


  Example: If we want to use high intensity white letters on blue background,
           we have to use the following color string:

                  "W+/B"   -->    "W"  White ForeColor
                                  "+"  High intensity ForeColor
                                  "B"  Blue BackColor


 At the MsDos hardware level, colors have the following structure:

                           Screen internal map

          <Char><Color><Char><Color><Char><Color><Char><Color>....

  Where <Char> is each of the characters we see on the screen and <Color>
  is the color of each character (attribute). Each <Color> is represented
  in only one byte.


      Binary representation
         of a byte color

    X  X  X  X  X  X  X  X    -->   Eight bits  ( = one byte )

    7  6  5  4  3  2  1  0          Bits order



        Bits N.
     =============

          7      -->  Back color intensity or Blinking
        6,5,4    -->  Back color
          3      -->  Fore color intensity
        2,1,0    -->  Fore color


  The color we specify as a string in xBase in translated -in MsDos- in
  one byte. Each xBase base color is a number from 0 to 7:

             Black ......... "N"  ....... 0  ..... 0 0 0
             Blue  ......... "B"  ....... 1  ..... 0 0 1
             Green ......... "G"  ....... 2  ..... 0 1 0
             Cyan  ......... "BG" ....... 3  ..... 0 1 1      Binary
             Red   ......... "R"  ....... 4  ..... 1 0 0   representation
             Magenta ....... "RB" ....... 5  ..... 1 0 1
             Brown ......... "GR" ....... 6  ..... 1 1 0
             White ......... "W"  ....... 7  ..... 1 1 1


 In the above example, we used "W+/B" to select High intensity white letters
 on blue background. So, when we see a character with that color on screen,
 that character has an associated byte with the value:

     xBase Color           HardWare color        Binary representation
     ===========           ==============        =====================

       "W+/B"                   31                  0 0 0 1 1 1 1 1


 Lets analyze the above binary representation:

     0 0 0 1 1 1 1 1    -->    0          0 0 1        1           1 1 1

     7 6 5 4 3 2 1 0         No Back    Blue Back     Fore       White Fore
     ( bits order )         Intensity     color     Intensity       Color