code: def to_s(indent=0)
           prefix = indent > 0 ? ' ' * indent : ''
           text   = StringIO.new
  
           text << "#{prefix}Colour Table (#{@colours.size} colours)"
           @colours.each {|colour| text << "\n#{prefix}   #{colour}"}
  
           text.string
        end
docs: This method generates a textual description for a ColourTable object.
  
   ==== Parameters
   indent::  The number of spaces to prefix to the lines generated by the
             method. Defaults to zero.