All the individuals who make up a particular angelic community have a general facial resemblance, but differ in detail. I could grasp this general similarity and particular difference to some extent on the basis of similar situations in this world. We know that every race has a general similarity about the face and eyes that enables us to recognize it and distinguish it from other races, and that the same is even more true from one family to another. This holds true much more perfectly in the heavens, because there all the deeper feelings are visible and shine forth from the face, the face there being their outward and graphic form. It is not possible in heaven to have a face that differs from our feelings.
I have also been shown how this general similarity is varied in detail in the individuals of a single community. There was a kind of angelic face that appeared to me, and this was varied according to the qualities of affections for the good and the true that were characteristic of the individuals in a particular community. These variations lasted quite a while, and through it all I noticed that the same general face remained constant as a basis, with everything else being simply derivations and elaborations from it. In this way, too, I was shown the affections of the whole community that occasioned the differences in the faces of its members, for as already noted, the faces of angels are their deeper qualities taking form, which means they are forms of the affections proper to their love and faith.
This is also why an angel of outstanding wisdom sees the quality of others instantly, from their faces. In heaven, no one can conceal inner character by facial expression and pretend, much less lie and deceive others by guile and hypocrisy.
It does sometimes happen that hypocrites steal into [heavenly] communities, hypocrites trained in hiding their inner nature and arranging their outward appearance in the benevolent form they present in public, thereby misleading angels of light. However, they cannot stay around very long. They begin to feel inner discomfort and torment, their faces start to turn blue, and they almost faint—changes caused by their opposition to the life that is flowing in and affecting them. So they promptly cast themselves back into the hell of people like themselves and no longer dare to climb up again. These are the people meant by the man who was discovered among the dinner guests without a wedding garment and was thrown out into outer darkness (Matthew 22:11).
from Heaven and Hell, Sections 47-48