I am not sure why I have a orange line when I imported a clip into iMovie

I have iMovie, The Missing Manual, First Edition, Fifth Release, by David Pogue and David Miller. On page 61 it reads: "Each time you add source video to your nascent movie, iMovie slaps an orange stripe across the bottom of the original clip in the Event browser, as shown in figure 5-8. That's a reminder that you've used this segment of footage in your project. As your work proceeds, you'll be able to tell, with a glance at your Event browser, what portion of the original video you used in your finished opus."