What key(s) or other command is used?

posted to: The Subdivide Tool

At 1:59 in the Subdivide Tool lesson in Section 5, the cube changes color from orange to gray, but although I've replayed that moment several times, I can't see what's done to change it. Assume it must be a keystroke, since practicing in my version of Blender with the different mouse buttons does nothing in this regard. Please advise. Thanks!  - Jonathan S.