def add(colour)
         if colour.instance_of?(Colour)
            @colours.push(colour) if @colours.index(colour).nil?
         end
         self
      end
def add(colour)
         if colour.instance_of?(Colour)
            @colours.push(colour) if @colours.index(colour).nil?
         end
         self
      end
This method adds a new colour to a ColourTable object. If the colour
 already exists within the table or is not a Colour object then this
 method does nothing.

 ==== Parameters
 colour::  The colour to be added to the table.