Num2Color()

         Converts a numeric color to string color

    Syntax:

         Color2Num ( nColor ) -> cColor

         nColor : The color in numeric format

    Description:

         Converts a color in numeric format into string format. The numeric
         color has to be a value between 0 and 255, both included.

    Return:

         The color in string format or Nil if the number is bigger than
         255 or smaller than 0.

    Example:

         ? Num2Color ( 31 )   // "W+/B"