Chart.js – add gradient instead of solid color – implementing solution

The link you provided was pretty clear, you have to put in the field fillColor in datasets a linearGradient object instead of a plain color. You can do complex gradients, but here is the code of a simple one (changing the opacity of the same orange) :

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

And your complete datasets :

datasets: [
            {
                fillColor : gradient, // Put the gradient here as a fill color
                strokeColor : "#ff6c23",
                pointColor : "#fff",
                pointStrokeColor : "#ff6c23",
                pointHighlightFill: "#fff",
                pointHighlightStroke: "#ff6c23",
                data : [25.0,32.4,22.2,39.4,34.2,22.0,23.2,24.1,20.0,18.4,19.1,17.4]
            }
        ]

See it in action in this JSFiddle