I recently tried this example to highlight my models:
bpmn-js-examples/colors at master · bpmn-io/bpmn-js-examples · GitHub
I was trying to use the viewer at first, but I discovered that it only works when using the modeler. The viewer does not have the “modeling” object needed for coloring. It would be nice if we could access this “modeling” object in the viewer too to apply coloring. For now, I can just use the modeler and just hide all the edit controls.