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CSS

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HTML 

              
                <ons-page>
  <ons-toolbar>
    <div class="center">Scroll toolbar background</div>
  </ons-toolbar>

  <div class="content">
    <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Aliquam semper sapien nec velit tempor rutrum. Nam at aliquet magna. Donec vestibulum velit laoreet sapien scelerisque bibendum. Vivamus vulputate arcu nisi. Suspendisse aliquam nisi non fringilla malesuada. In lacinia libero ac ligula porttitor, a pretium augue fermentum. Praesent egestas leo scelerisque, venenatis erat sit amet, pretium augue.
    </p>
    <p id="a">
    Nunc nulla velit, accumsan eu dictum nec, luctus quis nisi. Ut pulvinar vitae orci in efficitur. Donec eu sapien ultrices, imperdiet nulla vel, tincidunt quam. Donec convallis enim vel lectus condimentum, vitae ullamcorper nulla pretium. Ut egestas, diam eu fermentum ultrices, eros orci malesuada magna, eu maximus mi nulla ut felis. Nunc cursus dolor justo, at sodales ex fermentum quis. In bibendum sodales ex eget mollis. Praesent egestas egestas ipsum ac mollis. Sed faucibus tempus volutpat. Sed non dolor eleifend, placerat nibh et, blandit augue. Nunc eget nisl at dui vulputate iaculis ac sit amet erat. In in velit tempus, dictum dui non, pulvinar nisl. Nunc pretium risus vel nulla pharetra vestibulum.
    </p>
    <p id="b">
    Curabitur venenatis, arcu tincidunt rhoncus auctor, mauris ligula cursus justo, quis convallis lectus neque quis odio. Sed at libero condimentum leo congue pellentesque. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse luctus a odio vel tempus. Cras pellentesque odio sit amet orci laoreet mattis. Proin aliquam, dolor a lacinia elementum, sapien lectus posuere ex, sit amet porttitor urna quam eu augue. Etiam vitae pretium massa. Nulla at scelerisque ex.
    
    Duis facilisis augue nec neque tempor, eu tristique felis viverra. Nulla gravida tempor tellus ut tempor. Curabitur quis velit libero. Ut eu massa facilisis, tempus erat non, ullamcorper nunc. Morbi eget tortor semper, mollis tellus vitae, porta purus. Sed at augue vel nulla dignissim consequat quis vitae sem. Vestibulum laoreet turpis quis mauris fringilla, quis bibendum lacus placerat.

    Praesent lorem sem, sodales ac sollicitudin quis, mollis non dui. Aenean maximus in augue quis convallis. Proin pulvinar congue nisl, ut rutrum neque porta id. Praesent sapien ex, porttitor vitae diam eget, faucibus pretium lorem. In sed tempor mi. Cras faucibus finibus mi, in blandit mi efficitur nec. Nunc lorem tortor, accumsan et turpis vel, bibendum rhoncus quam. Suspendisse porttitor vel purus sit amet faucibus. Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Sed sapien dolor, consequat non scelerisque ac, pellentesque at quam. Aenean orci nunc, accumsan non neque sit amet, congue gravida turpis. Duis ac est et tellus imperdiet vulputate.

    Praesent lorem sem, sodales ac sollicitudin quis, mollis non dui. Aenean maximus in augue quis convallis. Proin pulvinar congue nisl, ut rutrum neque porta id. Praesent sapien ex, porttitor vitae diam eget, faucibus pretium lorem. In sed tempor mi. Cras faucibus finibus mi, in blandit mi efficitur nec. Nunc lorem tortor, accumsan et turpis vel, bibendum rhoncus quam. Suspendisse porttitor vel purus sit amet faucibus. Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Sed sapien dolor, consequat non scelerisque ac, pellentesque at quam. Aenean orci nunc, accumsan non neque sit amet, congue gravida turpis. Duis ac est et tellus imperdiet vulputate.

    Praesent lorem sem, sodales ac sollicitudin quis, mollis non dui. Aenean maximus in augue quis convallis. Proin pulvinar congue nisl, ut rutrum neque porta id. Praesent sapien ex, porttitor vitae diam eget, faucibus pretium lorem. In sed tempor mi. Cras faucibus finibus mi, in blandit mi efficitur nec. Nunc lorem tortor, accumsan et turpis vel, bibendum rhoncus quam. Suspendisse porttitor vel purus sit amet faucibus. Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Sed sapien dolor, consequat non scelerisque ac, pellentesque at quam. Aenean orci nunc, accumsan non neque sit amet, congue gravida turpis. Duis ac est et tellus imperdiet vulputate.

    Praesent lorem sem, sodales ac sollicitudin quis, mollis non dui. Aenean maximus in augue quis convallis. Proin pulvinar congue nisl, ut rutrum neque porta id. Praesent sapien ex, porttitor vitae diam eget, faucibus pretium lorem. In sed tempor mi. Cras faucibus finibus mi, in blandit mi efficitur nec. Nunc lorem tortor, accumsan et turpis vel, bibendum rhoncus quam. Suspendisse porttitor vel purus sit amet faucibus. Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Sed sapien dolor, consequat non scelerisque ac, pellentesque at quam. Aenean orci nunc, accumsan non neque sit amet, congue gravida turpis. Duis ac est et tellus imperdiet vulputate.
    </p>
  </div>
</ons-page>
!

CSS 

              
                ons-toolbar {
  transition: 0.2s background-color linear;
}
!

JS 

              
                ons.bootstrap();
var $ = document.querySelector.bind(document);
ons.ready(function(){
  var toolbar = $('ons-toolbar');
  var h = [$('#a').offsetTop, $('#b').offsetTop];
  var colors = ['white', 'lightblue', 'lightgreen'];
  var index = 0;
  $('.page__content').addEventListener('scroll', function(){
    var s = this.scrollTop;
    var newIndex = s < h[0] ? 0 : s < h[1] ? 1 : 2;
    if (index !== newIndex) {
      index = newIndex;
      toolbar.style.backgroundColor = colors[index];
    }
  });
});
!
999px

Console