how to remove text style on td in angularjs

var colorSpan = element(by.css('span'));

it('should check ng-style', function() {
  expect(colorSpan.getCssValue('color')).toMatch(/rgba\(0, 0, 0, 1\)|rgb\(0, 0, 0\)/);
  element(by.css('input[value=\'set color\']')).click();
  expect(colorSpan.getCssValue('color')).toMatch(/rgba\(255, 0, 0, 1\)|rgb\(255, 0, 0\)/);
  element(by.css('input[value=clear]')).click();
  expect(colorSpan.getCssValue('color')).toMatch(/rgba\(0, 0, 0, 1\)|rgb\(0, 0, 0\)/);
});<input type="button" value="set color" ng-click="myStyle={color:'red'}">
<input type="button" value="set background" ng-click="myStyle={'background-color':'blue'}">
<input type="button" value="clear" ng-click="myStyle={}">
<br/>
<span ng-style="myStyle">Sample Text</span>
<pre>myStyle={{myStyle}}</pre>span {
  color: black;
}