JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://rawgit.com/nnnick/Chart.js/v1.0.2/Chart.min.js"></script>
<canvas id="myChart" width="1200" height="400"></canvas>

JavaScript

Chart.types.Line.extend({
    name: "LineAlt",
    initialize: function (data) {
        Chart.types.Line.prototype.initialize.apply(this, arguments);

        // keep a reference to the original clear
        this.originalClear = this.clear;
        this.clear = function () {

            this.originalClear();

            // 1 x scale unit
            var unitX = this.datasets[0].points[1].x - this.datasets[0].points[0].x;

            var yTop = this.scale.startPoint;
            var yHeight = this.scale.endPoint - this.scale.startPoint;

            // change your color here
            this.chart.ctx.fillStyle = 'rgba(100,100,100,0.8)';

            // we shift it by half a x scale unit to the left because the space between gridline is actually a shared space
            this.chart.ctx.fillRect(this.datasets[0].points[5].x - 0.5 * unitX, yTop, unitX * 5, yHeight);
            this.chart.ctx.fillRect(this.datasets[0].points[15].x - 0.5 * unitX, yTop, unitX * 5, yHeight);
        }
    }
});


var data = {
    labels: ["Mon", "Tue", "Wed", "Thu", "Fri", "Mon", "Tue", "Wed", "Thu", "Fri", "Mon", "Tue", "Wed", "Thu", "Fri", "Mon", "Tue", "Wed", "Thu", "Fri"],
    datasets: [{
        label: "My First dataset",
        fillColor: "rgba(220,220,220,0.2)",
        strokeColor: "rgba(220,220,220,1)",
        pointColor: "rgba(220,220,220,1)",
        pointStrokeColor: "#fff",
        pointHighlightFill: "#fff",
        pointHighlightStroke: "rgba(220,220,220,1)",
        data: [65, 59, 80, 81, 56, 65, 59, 80, 81, 56, 65, 59, 80, 81, 56, 65, 59, 80, 81, 56]
    }, {
        label: "My Second dataset",
        fillColor: "rgba(151,187,205,0.2)",
        strokeColor: "rgba(151,187,205,1)",
        pointColor: "rgba(151,187,205,1)",
        pointStrokeColor: "#fff",
        pointHighlightFill: "#fff",
        pointHighlightStroke: "rgba(151,187,205,1)",
        data: [28, 48, 40, 19, 86, 28, 48, 40, 19, 86, 28, 48, 40, 19, 86, 28, 48, 40, 19, 86]
    }]
};

var ctx =...