I know that they can do it, but what would it look like, or is it unseeable?
Think about how vision works: We "see" light that strikes our eyeballs after bouncing off of objects. The light is an electric pulse that stimulates a current in our eye and brain.
That said, frozen light (which I have heard of but do not actually know about) does not actual reach our eyeball if it is indeed frozen, and so we cannot see it.
Here's an article about it
Essentially it seems the photons aren't really stopped they are bounced back and forward between the equivalent of 2 mirrors.
Separate names with a comma.