code: function rollbackDefaultTextStyle(style) {
      var insideRollback = style.insideRollback;
      if (insideRollback) {
          style.textFill = insideRollback.textFill;
          style.textStroke = insideRollback.textStroke;
          style.textStrokeWidth = insideRollback.textStrokeWidth;
          style.insideRollback = null;
      }
  }
docs: Consider the case: in a scatter,
  label: {
  normal: {position: 'inside'},
  emphasis: {position: 'top'}
  }
  In the normal state, the `textFill` will be set as '#fff' for pretty view (see
  `applyDefaultTextStyle`), but when switching to emphasis state, the `textFill`
  should be retured to 'autoColor', but not keep '#fff'.