changeColor_() {
    if (this.color_ == 'red') {
      this.color_ = 'green';
    } else if (this.color_ == 'green') {
      this.color_ = 'blue';
    } else {
      this.color_ = 'red';
    }
    this.getElement().style.backgroundColor = this.color_;
  }
Changes the color of the element.
@private