def to_array(color_model = :rgb)
      color_model = color_model.to_sym unless color_model.is_a? Symbol
      if [:rgb, :hsl].include?(color_model)
        array = colors.map { |c| c.to_array(color_model) }
      elsif color_model == :hex
        array = colors.map{ |c| c.hex }
      else
        raise(ArgumentError, "Argument must be :rgb, :hsl, or :hex")
      end
      array
    end
def to_array(color_model = :rgb)
      color_model = color_model.to_sym unless color_model.is_a? Symbol
      if [:rgb, :hsl].include?(color_model)
        array = colors.map { |c| c.to_array(color_model) }
      elsif color_model == :hex
        array = colors.map{ |c| c.hex }
      else
        raise(ArgumentError, "Argument must be :rgb, :hsl, or :hex")
      end
      array
    end
Return an array representation of a {Palette} instance,
 @param [Symbol] model the color model, should be :rgb, :hsl, or :hex
 @return [Array] an Array of Arrays where each sub-Array is a representation of a {Color} object in a {Palette} instance