[解決済み] CSSを使用して、個々のセルに色を付けずにテーブルの列を着色することはできますか？

<table border="1">
  <tr>
    <th>Motor</th>
    <th colspan="3">Engine</th>
    <th>Car</th>
    <th colspan="2">Body</th>
  </tr>
  <tr>
    <td>1</td>
    <td>2</td>
    <td>3</td>
    <td>4</td>
    <td>5</td>
    <td>6</td>
    <td>7</td>
  </tr>
  <tr>
    <td>7</td>
    <td>1</td>
    <td>2</td>
    <td>3</td>
    <td>4</td>
    <td>5</td>
    <td>6</td>
  </tr>
</table>

<style>
  .color {
    background-color: #DDD
  }
</style>
<table border="1">
  <tr>
    <th>Motor</th>
    <th colspan="3" class="color">Engine</th>
    <th>Car</th>
    <th colspan="2" class="color">Body</th>
  </tr>
  <tr>
    <td>1</td>
    <td class="color">2</td>
    <td class="color">3</td>
    <td class="color">4</td>
    <td>5</td>
    <td class="color">6</td>
    <td class="color">7</td>
  </tr>
  <tr>
    <td>7</td>
    <td class="color">1</td>
    <td class="color">2</td>
    <td class="color">3</td>
    <td>4</td>
    <td class="color">5</td>
    <td class="color">6</td>
  </tr>
</table>

.grey {
  background-color: rgba(128,128,128,.25);
}
.red {
  background-color: rgba(255,0,0,.25);
}
.blue {
  background-color: rgba(0,0,255,.25);
}

<table>
  <colgroup>
    <col class="grey" />
    <col class="red" span="3" />
    <col class="blue" />
  </colgroup>
  <thead>
    <tr>
      <th>#</th>
      <th colspan="3">color 1</th>
      <th>color 2</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th>1</th>
      <td>red</td>
      <td>red</td>
      <td>red</td>
      <td>blue</td>
    </tr>
    <tr>
      <th>2</th>
      <td>red</td>
      <td>red</td>
      <td>red</td>      
      <td>blue</td>
    </tr>
  </tbody>
</table>