def color
      case speed
      when 0..3 then
        '#000000'
      when 4..7 then
        '#330000'
      when 8..10 then
        '#660000'
      when 11..14 then
        '#990000'
      when 15..17 then
        '#cc0000'
      when 18..21 then
        '#ff0000'
      when 22..24 then
        '#ff3300'
      when 25..28 then
        '#ff6600'
      when 29..31 then
        '#ff9900'
      when 32..34 then
        '#ffcc00'
      when 35..38 then
        '#ffff00'
      when 39..41 then
        '#ccff00'
      when 42..45 then
        '#99ff00'
      when 46..48 then
        '#66ff00'
      when 49..52 then
        '#33ff00'
      when 53..90 then
        '#00ff00'
      else
        '#999999'
      end
  end