After a "minor mistake" made by Gabriel, he Dean, Sam and Castiel teleported into another universe. A different universe. Walking on the streets of New York, the sky opened and they were dragged into Heaven. Here, they found out in that universe there's not a single hunter and the ones who were taking care of humans and hunted supernatural creatures were angels and demons. Crazy, right? And here "the special humans" could become angels or demons, being enrolled in the "Celestials College". So ironic. And plus here the wings were visible so now Sam and Dean could see Castiel and Gabriel's wings. Castiel's ones were light gray and Gabriel's were a bit bigger and milky white.