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

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

var gradient = ctx.createLinearGradient(0, 0, 0, 400);
gradient.addColorStop(0, 'rgba(250,174,50,1)');   
gradient.addColorStop(1, 'rgba(250,174,50,0)');

var gradient2 = ctx.createLinearGradient(0, 0, 400, 0);
gradient2.addColorStop(0, 'rgba(174,250,50,1)');   
gradient2.addColorStop(1, 'rgba(174,50,250,1)');


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: true,
      borderColor: gradient2,
      backgroundColor: gradient
    }]
  },
  options: {
    legend: {
    	display: false
    },
  	tooltips: {
    	callbacks: {
      	label: function(tooltipItem) {
        console.log(tooltipItem)
        	return tooltipItem.yLabel;
        }
      }
    }
  }
};

new Chart(ctx, config);