用js生成rgb颜色

    var drawing=document.getElementById("drawing");
    drawing.onclick= function () {
        var x, y, z;
        x=Math.floor(Math.random()*256);
        y=Math.floor(Math.random()*256);
        z=Math.floor(Math.random()*256);
        drawing.style.background='rgba('+x+','+y+','+z+','+1+')';
    }

<canvas id="drawing" width="200" height="200">A drawing of something.</canvas>