I noticed that in the first part of your presentation the instance of VisualVM itself was visible, together with its corresponding icon. However, when you were developing a new plugin, and VisualVM was started from within NetBeans IDE, it was NetBeans IDE's icon that was displayed, while I was expecting to see VisualVM's icon here too, because you're developing against the VisualVM instance of the platform. What am I missing here?
Not only the icon is affected, but also the splash screen and the text in the titlebar. The way to fix this is to add this line to either platform.properties or project.properties, of the NetBeans module that you're running from the IDE:
Above, the branding token is set, which specifies the branding information that should be used when the selected platform is started. What would be even better, I think, would be that when you change the NetBeans Platform for a particular module, the platform.properties or project.properties file should be automatically updated with the above key/value combination.
Anyway, simply adding the branding token of the platform you're running against, in this case VisualVM, is enough to ensure that when the module is run from the IDE, which then causes the platform to start, the correct icon, titlebar, and splash screen will be displayed.