<!DOCTYPE html>
<html>
<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.4.8/angular.min.js"></script>
<style>
form.ng-pristine {
background-color:lightblue;
}
form.ng-dirty {
background-color:pink;
}
</style>
<body ng-app="">
<form name="myForm">
<p>Try writing in the input field:</p>
<input name="myName" ng-model="myName" required>
<p>The form gets a "ng-dirty" class when the form has been modified, and will therefore turn pink.</p>
</form>
</body>
</html>