What does the grey area in the Customizer mean?

Grey area in the Customizer is the device template where you can upload pictures, text, shapes, and background colors to design your Skin.  If the grey portion is left blank then the final Skin will print grey. While Customizing the Skin we recommend that the entire grey area is covered with the design of your choice.

For more help designing your Skin please refer to the tutorial videos located in the Customizer.