Can I color table columns using CSS without coloring individual cells?

.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>