Hello again,
If this script posted above is attached on the same gameobject as the FlowScriptController that you are sending the event is, then it should really work. I think it already does, but the thing that probably made up for the confusion is the fact that your color ALPHA in the Set Color node is 0 (full transparent). Could this be the case?
Also, have you tried with a simple Debug Text or Debug Value node just to make sure it does or does not work?