_makePickerButtonElement(defaultColor) {
    this.colorpickerElement.classList.add('tui-image-editor-button');

    this.colorElement = document.createElement('div');
    this.colorElement.className = 'color-picker-value';
    if (defaultColor) {
      this.colorElement.style.backgroundColor = defaultColor;
    } else {
      this.colorElement.classList.add('transparent');
    }
  }
Make picker button element
@param {string} defaultColor color value
@private