I am a bit of a novice with Blender, but I seem to have most things set straight. Absolutely love the software by the way. I am currently designing an iPhone 7 concept. But, something that has stunned my progress is the fact that the Subdivision Surface (Catmull-Clark) modifier applied to the phone has made an ugly appearance on the phone's back. I have attached two pictures to this to better show what I mean. The first screen shot shows the phone's back in Textured view during Object Mode, and the other in Wireframe during Editing Mode. I don't understand why there is such a repulsive shape on the back of the phone while the front looks amazing. The shape for some reason is emitting a bright white color. I am not sure whether this is a bug in need of fixing or if I have done something wrong. I appreciate your help. Thank you.