function random_rgba() {
    var o = Math.round, r = Math.random, s = 255;
    return 'rgba(' + o(r()*s) + ',' + o(r()*s) + ',' + o(r()*s) + ',' + r().toFixed(1) + ')';
}

var color = random_rgba();

g.fillStyle   = color;
g.strokeStyle = color;