S.Color = function (r, g, b, a) {
  this.r = r;
  this.g = g;
  this.b = b;
  this.a = a;
};

S.Color.prototype = {
  render: function () {
    return 'rgba(' + this.r + ',' + this.g + ',' + this.b + ',' + this.a + ')';
  }
};