The red line isn't always red. And it isn't always a line. Any color or re-occurring theme will do. Several people standing at an ATM line all wearing clothing in the purple family. A women sitting on the blue seat of a subway in a blue coat, carrying a blue suitcase, with a Jetblue advertisement behind her. When we wake up and take notice, we realize that seeing is not the same as looking and the "red line" really is everywhere.