def theme=(options)
      reset_themes

      defaults = {
          :colors => %w(black white),
          :additional_line_colors => [],
          :marker_color => 'white',
          :marker_shadow_color => nil,
          :font_color => 'black',
          :background_colors => nil,
          :background_image => nil
      }
      @theme_options = defaults.merge options

      @colors = @theme_options[:colors]
      @marker_color = @theme_options[:marker_color]
      @marker_shadow_color = @theme_options[:marker_shadow_color]
      @font_color = @theme_options[:font_color] || @marker_color
      @additional_line_colors = @theme_options[:additional_line_colors]

      render_background
    end
def theme=(options)
      reset_themes

      defaults = {
          :colors => %w(black white),
          :additional_line_colors => [],
          :marker_color => 'white',
          :marker_shadow_color => nil,
          :font_color => 'black',
          :background_colors => nil,
          :background_image => nil
      }
      @theme_options = defaults.merge options

      @colors = @theme_options[:colors]
      @marker_color = @theme_options[:marker_color]
      @marker_shadow_color = @theme_options[:marker_shadow_color]
      @font_color = @theme_options[:font_color] || @marker_color
      @additional_line_colors = @theme_options[:additional_line_colors]

      render_background
    end
You can set a theme manually. Assign a hash to this method before you
 send your data.

  graph.theme = {
    :colors => %w(orange purple green white red),
    :marker_color => 'blue',
    :background_colors => ['black', 'grey', :top_bottom]
  }

 :background_image => 'squirrel.png' is also possible.

 (Or hopefully something better looking than that.)