Objection 1. It would seem that a glorified body will be necessarily seen by a non-glorified body. For the glorified bodies will be lightsome. Now a lightsome body reveals itself and other things. Therefore the glorified bodies will be seen of necessity.
Objection 2. Further, every body which hides other bodies that are behind it is necessarily perceived by the sight, from the very fact that the other things behind it are hidden. Now the glorified body will hide other bodies that are behind it from being seen, because it will be a colored body. Therefore it will be seen of necessity.
Objection 3. Further, just as quantity is something in a body, so is the quality whereby a body is seen. Now quantity will not be subject to the will, so that the glorified body be able to be of greater or smaller quantity. Therefore neither will the quality of visibility be subject to the will, so that a body be able not to be seen.
On the contrary, Our body will be glorified in being made like to the body of Christ after the resurrection. Now after the resurrection Christ's body was not necessarily seen; in fact it vanished from the sight of the disciples at Emmaus (Luke 24:31). Therefore neither will the glorified body be necessarily seen.
Further, there the body will be in complete obedience to the will. Therefore as the soul lists the body will be visible or invisible.
I answer that, A visible object is seen, inasmuch as it acts on the sight. Now there is no change in a thing through its acting or not acting on an external object. Wherefore a glorified body may be seen or not seen without any property pertaining to its perfection being changed. Consequently it will be in the power of a glorified soul for its body to be seen or not seen, even as any other action of the body will be in the soul's power; else the glorified body would not be a perfectly obedient instrument of its principal agent.
Reply to Objection 1. This clarity will be obedient to the glorified body so that this will be able to show it or hide it.
Reply to Objection 2. A body's color does not prevent its being transparent except in so far as it affects the sight, because the sight cannot be affected by two colors at the same time, so as to perceive them both perfectly. But the color of the glorified body will be completely in the power of the soul, so that it can thereby act or not act on the sight. Hence it will be in its power to hide or not to hide a body that is behind it.
Reply to Objection 3. Quantity is inherent to the glorified body itself, nor would it be possible for the quantity to be altered at the soul's bidding without the glorified body suffering some alteration incompatible with its impassibility. Hence there is no comparison between quantity and visibility, because even this quality whereby it is visible cannot be removed at the soul's bidding, but the action of that quality will be suspended, and thus the body will be hidden at the soul's command.
Source: Summa Theologica (New Advent)