If Else Statement using ELM

I am looking to change specific div colors oclick to either blue or grey - There are a number of different divs under the same class and I want to be able to click on each one individually to change the color to either blue or grey

          <div class="sidebar2" onclick="change(this)">
          <p>11</p>
          </div>
          <div class="sidebar2" onclick="change(this)">
          <p>10</p>
          </div>
          <div class="sidebar2" onclick="change(this)">
          <p>9</p>
          </div>
          <div class="sidebar2" onclick="change(this)">
          <p>8</p>
          </div>


    <!-- JavaScript -->

    <script>
    function change(elm) {
    elm.style.backgroundColor = '#1E90FF'
    }
    </script>