The purple border is there because you're using an "End Workflow" activity to complete this workflow. Because it is inside the Business Process Step, the step technically does not finish running and therefore becomes "Canceled" when End Workflow sends the signal to complete. This is normal behavior. 

Note: I can't see the other end of your workflow, but if there aren't other activities after the End Workflow and it always stops this way, then you can safely just let the workflow end naturally and the purple borders will go away.