chart.js 2.1

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.1.0/Chart.bundle.min.js"></script>
<canvas id="myChart"></canvas>

JavaScript

Chart.pluginService.register({
			beforeDraw: function (chart, easing) {
				if (chart.config.options.chartArea && chart.config.options.chartArea.backgroundColor) {
					var helpers = Chart.helpers;
					var ctx = chart.chart.ctx;
					var chartArea = chart.chartArea;

          var columnCount = chart.data.datasets[0].data.length;
          var width = chartArea.right - chartArea.left;
          var height = chartArea.bottom - chartArea.top

					var columnWidth = width/columnCount;
					ctx.save();
					ctx.fillStyle = chart.config.options.chartArea.backgroundColor;
          var startPoint = chartArea.left
          while (startPoint < chartArea.right) {
          	ctx.fillRect(startPoint, chartArea.top, columnWidth, height);
            startPoint += columnWidth * 2;
          }
					ctx.restore();
				}
			}
		});

		var config = {
			type: 'line',
			data: {
				labels: ["January", "February", "March", "April", "May", "June", "July"],
				datasets: [{
					label: "My First dataset",
					data: [65, 0, 80, 81, 56, 85, 40],
					fill: false
				}]
			},
			options: {
				chartArea: {
					backgroundColor: 'rgba(251, 85, 85, 0.4)'
				}
			}
		};

		var ctx = document.getElementById("myChart").getContext("2d");
		new Chart(ctx, config);