The followings are some examples to change the chart. (They add/remove lines or symbols on the chart. The method is the same for any other kinds of changes to the chart.)
In brief, you need some method to tell the server which labels should be in another color. There are several methods. The exact details depend on your web framework (eg. ASP.NET or ASP.NET Core or ASP.NET MVC ....).
In the zoomscrolltrackweb example, it stores the necessary information in custom attributes, and then it sends a "partialUpdate" request to the server. The server code is designed to handle this request and redraw the chart according to the attributes.
In the financedemo example, it just uses traditional POST to send the status of the controls to the server. You can add hidden fields to store additional information, such as the labels that need to change color.