function save() {
    let data = {
          datasets: myChart.data.datasets
     };
     $.post('/save',
         {
             savedData: JSON.stringify(data),
             color: document.getElementById("color").value,
             ...
         }
      )
}

require(["dojox/json/ref"], function(){
    let data = {
            datasets: dojox.json.ref.toJson(...)
    }
    $.post('/save',
    ...
});

require(["dojox/json/ref"], function(){
      data = dojox.json.ref.fromJson(...);
});

<script src="//ajax.googleapis.com/ajax/libs/dojo/1.13.0/dojo/dojo.js"></script>