Nodes sometimes get a pink border, which means that they are throwing a runtime error. Hovering the node with the tooltip will show you more information about the error:
Depending on your Setting for "Pause on Error" the execution of your patch will either pause or continue. But even if the execution continues it may fail again at the same spot at a later time. Therefore it is good practise, to "handle" exceptions.
In order to handle runtime errors programmatically, you can surround the culprit with a Try region:
This will allow you to react to problems in your patch gracefully without interrupting the execution of your program.