要素の背景色コードを16進数で取得する方法は？

console.log($(".div").css("background-color"));

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="div" style="background-color: #f5b405"></div>

var color = '';
$('div').click(function() {
  var x = $(this).css('backgroundColor');
  hexc(x);
  console.log(color);
})

function hexc(colorval) {
  var parts = colorval.match(/^rgb\((\d+),\s*(\d+),\s*(\d+)\)$/);
  delete(parts[0]);
  for (var i = 1; i <= 3; ++i) {
    parts[i] = parseInt(parts[i]).toString(16);
    if (parts[i].length == 1) parts[i] = '0' + parts[i];
  }
  color = '#' + parts.join('');
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class='div' style='background-color: #f5b405'>Click me!</div>