如何绘制chartJs的特定区域？

<canvas id="myChart"></canvas>

var ctx = document.getElementById('myChart').getContext('2d');

var data = {
  labels: ['Red', 'Blue', 'Yellow', 'Green', 'Purple', 'Orange'],
  datasets: [{
    label: 'My Dataset',
    data: [12, 19, 3, 5, 2, 3],
    backgroundColor: 'rgba(255, 99, 132, 0.2)',
    borderColor: 'rgba(255, 99, 132, 1)',
    borderWidth: 1
  }]
};

var options = {
  scales: {
    y: {
      beginAtZero: true
    }
  }
};

var myChart = new Chart(ctx, {
  type: 'bar',
  data: data,
  options: options
});