During the scene in Abby's office when Mike is coaching her through her phone call after they make their deal, Mike tells her to put Colin on hold. She does so and the button for his call turns from a red light to a blinking green light. After a few angle changes with the camera, there is one shot over Abby's shoulder and you see the phones light is red and not blinking green. Then right when Abby is about to take Colin off hold and the camera is only on the phone, the light has returned from red to blinking green again.