In this tutorial Blender is in the mode that I want, but I cant find the theme.
I think the question is really: how do you make the cube appear transparent, so that you can see the background image whilst editing?
It is simply that in the screenshot from youtube, the user is in edit mode (press 'tab') with wireframe display mode (press 'z') and all vertices selected (press 'a').
You can change Blender Themes colors under "File>User Preferences>Themes" in Blender 2.7X or "Edit>User Preferences>Themes" in Blender 2.8.
This screenshot is from Blender 2.79
Make sure you select 3D View, then scroll down to find "Active Vert/Edge/Face", here you can change the color and opacity of selected mesh elements.
Same steps in Blender 2.8, except that user preferences is under Edit drop-down menu, and the panel will look different.